Implements focus traversal for desktop platforms, including re-implementing the existing focus manager and focus tree.

This implements a Focus widget that can be put into a widget tree to allow input focus to be given to a particular part of a widget tree.

It incorporates with the existing FocusScope and FocusNode infrastructure, and has minimal breakage to the API, although FocusScope.reparentIfNeeded is removed, replaced by a call to FocusAttachment.reparent(), so this is a breaking change:

FocusScopeNodes must now be attached to the focus tree using FocusScopeNode.attach, which takes a context and an optional onKey callback, and returns a FocusAttachment that should be kept by the widget that hosts the FocusScopeNode. This is necessary because of the need to make sure that the focus tree reflects the widget hierarchy.

Callers that used to call FocusScope(context).reparentIfNeeded in their build method will call reparent  on a FocusAttachment instead, which they will obtain by calling FocusScopeNode.attach in their initState method. Widgets that own FocusNodes will need to call dispose on the focus node in their dispose method.

Addresses #11344, #1608, #13264, and #1678
Fixes #30084
Fixes #26704

* rectMoreOrLess equals, prep for 64bit rects

* Add track-widget-creation flag to attach command

* use the flag

TextField and CupertinoTextField can now specify scrollPhysics. Cupertino defaults to bouncing now.

Revert "[Material] Update slider and slider theme with new sizes, shapes, and color mappings (#30390)" (#31339)

This reverts commit b1039f0f.

(This is a temporary revert while some of our customers deal with the breaking changes involved.)

* add attach.md document

* Added support for authentication codes for the VM service.

Previously, a valid web socket connection would use the following URI:

`ws://127.0.0.1/ws`

Now, by default, the VM service requires a connection to be made with a
URI similar to the following:

`ws://127.0.0.1:8181/Ug_U0QVsqFs=/ws`

where `Ug_U0QVsqFs` is an authentication code generated and shared by
the
service.

This behavior can be disabled with the `--disable-service-auth-codes`
flag.

* add daemon.log to the daemon spec

* mention use in flutter run --machine

The 'doctor' check to determine if any devices can be listed for the
device should consider desktop workflows as well.

This has no effect unless the environment variable to enable desktop
device listing is set.

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.

https://github.com/flutter/engine/compare/06fea14e5800...4b9966f5cb41

git log 06fea14e5800c35a4fc4dd10cc31b997f1be81e9..4b9966f5cb412a73fa50462b3aee9082f436a62a --no-merges --oneline
4b9966f5c Add an adjustment to the line width check in LineBreaker::addWordBreak (flutter/engine#8623)
60bb866ce Roll src/third_party/skia a94670bd08cd..2c2240f66805 (2 commits) (flutter/engine#8632)
a144f17ae Tight Paragraph Width (flutter/engine#8530)

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https://github.com/flutter/engine/compare/b6787096a2d3...06fea14e5800

git log b6787096a2d3d0365f03f4cfdb70b932e4e5bae3..06fea14e5800c35a4fc4dd10cc31b997f1be81e9 --no-merges --oneline
06fea14e5 Glitchiness with Tab Characters (flutter/engine#8591)

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b6787096a Roll src/third_party/skia 847d55be4e62..a94670bd08cd (1 commits) (flutter/engine#8631) (#31260)


https://github.com/flutter/engine/compare/3e6dc02ad62e...b6787096a2d3

git log 3e6dc02ad62ef9fa02660f5fb0bb114414e282d4..b6787096a2d3d0365f03f4cfdb70b932e4e5bae3 --no-merges --oneline
b6787096a Roll src/third_party/skia 847d55be4e62..a94670bd08cd (1 commits) (flutter/engine#8631)

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3e6dc02ad Roll src/third_party/skia ced2b79d00f9..847d55be4e62 (3 commits) (flutter/engine#8630) (#31251)


https://github.com/flutter/engine/compare/54f7c51339ae...3e6dc02ad62e

git log 54f7c51339ae7d86a983b5850b14dafe4e2bd90a..3e6dc02ad62ef9fa02660f5fb0bb114414e282d4 --no-merges --oneline
3e6dc02ad Roll src/third_party/skia ced2b79d00f9..847d55be4e62 (3 commits) (flutter/engine#8630)

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54f7c5133 Roll src/third_party/skia 14c90c1ca218..ced2b79d00f9 (1 commits) (flutter/engine#8629) (#31240)


https://github.com/flutter/engine/compare/70068706d0ee...54f7c51339ae

git log 70068706d0ee3bc9847632c4d0e467fba49271f8..54f7c51339ae7d86a983b5850b14dafe4e2bd90a --no-merges --oneline
54f7c5133 Roll src/third_party/skia 14c90c1ca218..ced2b79d00f9 (1 commits) (flutter/engine#8629)

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https://github.com/flutter/engine/compare/8b5a50c0df76...70068706d0ee

git log 8b5a50c0df768743dd9858cceb92d1d1de44c35e..70068706d0ee3bc9847632c4d0e467fba49271f8 --no-merges --oneline
70068706d Allow building without python2 (flutter/engine#8605)

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https://github.com/flutter/engine/compare/876c4c339064...8b5a50c0df76

git log 876c4c339064ed321f37fba61422194d84cbfdb7..8b5a50c0df768743dd9858cceb92d1d1de44c35e --no-merges --oneline
8b5a50c0d Test saving compilation traces. (flutter/engine#8618)
7d3caf895 Avoid leaking the VM in runtime_unittests and update failing tests. (flutter/engine#8626)
91b71070f Revert "Add a unit test for PhysicalShapeLayer (#8616)" (flutter/engine#8627)
8b667b017 Add a unit test for PhysicalShapeLayer (flutter/engine#8616)

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https://github.com/flutter/engine/compare/76794745b676...876c4c339064

git log 76794745b6764246cffafb237182f7fafeac41f8..876c4c339064ed321f37fba61422194d84cbfdb7 --no-merges --oneline
876c4c339 Assert that all VM launches in the process have the same opinion on whether the VM should be leaked in the process. (flutter/engine#8622)
72c84c287 Revert "Roll src/third_party/dart 7b9ab9f353..714a082a5d (7 commits)" (flutter/engine#8624)
f017fe74a Avoid manually shutting down engine managed isolates. (flutter/engine#8621)
80e934e32 Roll src/third_party/dart 7b9ab9f353..714a082a5d (7 commits)

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https://github.com/flutter/engine/compare/523a9a9adde9...76794745b676

git log 523a9a9adde96d22c801eac59f9f6db3d2a79a30..76794745b6764246cffafb237182f7fafeac41f8 --no-merges --oneline
76794745b Roll src/third_party/skia 6f9047027be3..14c90c1ca218 (5 commits) (flutter/engine#8619)
d8aa6bca1 Fix typo in comment (flutter/engine#8617)
8ff631f3d Rename flow namespace to flutter (flutter/engine#8615)
0534b6ae5 Roll src/third_party/dart bc99f1ca28..7b9ab9f353 (5 commits)
b767e4d3c Roll src/third_party/skia 5155e09d1466..6f9047027be3 (5 commits) (flutter/engine#8613)
c5d1ba916 Remove call to SkFont::setLinearMetrics (flutter/engine#8612)

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Will cause golden and Scuba changes. Caret will become taller and shift upwards by 2 pixels.