Also switched to relative paths for local packages.

* create auto back button behaviour

* cosmetic fidelity

* tests

* review

* document new icon

This refactoring allows us to have SemanticsEvent object for events that are not
associated with an accessibility node id.
And allow https://github.com/flutter/flutter/pull/12594 to be a bit
cleaner with a single place for accessibility channel documentation (the
SemanticsEvent classes documentation).

* Revert "BoxDecoration.borderRadius and RoundedRectangleBorder.borderRadius RTL (#12603)"

This reverts commit 07908916.

* Revert "Copy snapshot file into assets (#12523)"

This reverts commit f6135107.

* Revert "Add a rootNavigator option to Navigator.of (#12580)"

This reverts commit 822084b2.

* Revert "Fix error message to refer to actual ClipRect widget instead of non-existing RectClip (#12632)"

This reverts commit 1573d3b8.

* Revert "Roll engine to 5003703330f280325fa73080bb23b1ab7008b213 (#12629)"

This reverts commit 81a358b7.

* Make clean command top level

Fixes https://github.com/flutter/flutter/issues/10783

* remove backwards

The libimobiledevice suite of tools do not include version information.
A simple way to verify they meet our version requirements is to run
idevice_id -l, which will fail when older versions are run against iOS
devices with newer versions of iOS installed.

Unfortunately, idevice_id -l will also fail when libimobiledevice is up
to date, but the attached devices have never been paired with the host
machine in Xcode.

This patch updates the error message to help guide the user in such
situations.

Fixes InputDecorator to work with textScaleFactor, fixes Material Design differences.

There were a number of differences with the Material Design spec, including
several different padding values and underline thickness.  This corrects
that so that the decorator is in line with the Material Design spec now.

Also, the decorator properly handles changes to the textScaleFactor, where
before it would not re-layout when needed, painting the cursor and
underline incorrectly.

The decorator also now properly animates helper, error, and hint text when
the textScaleFactor or input decoration properties change.

Helper text is now properly displayed in dense mode, as the spec shows.
Before this change, it was never displayed in dense mode.

Fixes #12485

Hixie pointed out that what I had before was resetting all of the MediaQuery values, not just textScaleFactor. This should fix that.

Syncing source files is not needed when host sends kernel file to the device.

This aids in running the tests internally in Google
since the libraries upon which tests depend and the
test files themselves are defined separately.

Merge confliuct between #12605 and #12613

* Oct 12 10:12am

* implicit_semantics_test.dart passes

* refactoring

* works in nice

* minor rename

* more doc comments

* to be explicit check better

* fix test

* ++

* ++

* semantics_9_test (BlockSemantics) and implicit_semantics_test are passing

* doc updates

* tiny refactor

* fix static errors in tests

* fix gesture detector

* ++

* ++

* geometry

* ++

* remove noGeometry

* revert test

* +

* all tests but scrolling/clipping pass

* clipping works

* scrolling halfway

* sliver tests pass

* ALL TESTS PASS

* SemanticsNode changed

* docs and tiny fixes

* card test

* more doc comments

* remove missed print

* more tests

* make test pass on Linux

* remove changes to intellij proj file

* review comments

* Make Tab take a widget as child

This way you can override the semantics information of a Tab (see test).

Fixes https://github.com/flutter/flutter/issues/12432

* more tests

* review comments

* review comment

* doc nits

* style fix

On iOS 11.0.x ideviceinfo fails with the following message
ERROR: Could not connect to lockdownd, error code -3

This workaround should also work for #12330

libtxt's implementation of Paragraph.getBoxesForRange returns the full line
height for all characters in a line.  Blink had been returning a tighter
enclosing rectangle for each individual character.

This patch also makes it possible to create FLX files with no extension.
Previously, the zip tool would add the ".zip" extension if the output file
lacked an extension.

libtxt has different policies than Blink for trimming whitespace.  This change
will make the test results consistent in both text renderers.