* Do not crash when toggeling Semantics on, off, on

* review comments

Fixes https://github.com/flutter/flutter/issues/12553

The root cause of https://github.com/flutter/flutter/issues/12553 was that when the refresh indicator went away, which happened after the avatars had started their image loads but before the avatars had loaded, the DecoratedBoxes, along with the rest of the list, got GlobalKey-reparented, which caused the RenderDecoratedBox objects to unregister from the DecorationImagePainters, but they never re-registered since the whole subtree was in a RepaintBoundary and was therefore not explicitly repainted when the tree got reattached.

This fixes the bug by explicitly requiring any RenderDecoratedBox to repaint when it's reattached. This is probably a little more aggressive than required; we could probably expose a flag on Decoration that says whether or not the onChanged handler will ever be invoked, and only call markNeedsPaint if that's true, but we'll do that if it turns out that there's a performance issue here.

(This patch also introduces a bunch of improved debugging information that I used to track down the bug.)

* Revert "Fixed output validation. (#14005)"

This reverts commit d84398db.

* Revert "Update package prep script to do async process execution and emit output as it happens. (#13918)"

This reverts commit b7169c1d.

 - Switches to async process execution, which now shows output as it happens instead of in chunks when the process completes
-  Now uses ProcessManager so that it may be mocked for the test.
- Adds in the download and install of mingit on Windows.
- Updated package dependencies because of added dependency on process package.

* Lock events during runApp's warm up frame

* move to scheduler binding

* let the one scheduleWarmUpFrame api always lock

* tweak test

`RenderSemanticsGestureHandler` is no longer a semantics boundary, which allows us to correctly mark disabled buttons as disabled without having their semantics size and semantics node id change unexpectedly.

Fixes https://github.com/flutter/flutter/issues/12589.
Fixes https://github.com/flutter/flutter/issues/11991.
See also https://github.com/flutter/flutter/issues/11993.

This change also required some refactoring to how we deal with `twoPaneSemantics` scrolling as it previously relied on `RenderSemanticsGestureHandler` being a semantics boundary. This should also make the underlying logic easier to understand.

In addition, the following minor changes are included in this PR:
* Removal of orphaned and unused `SemanticsConfiguration.isMergingDescendantsIntoOneNode`.
* Logic optimizations for `markNeedsSemanticsUpdate` .
* Fix for edge case where `MergeSemantics` failed to merge semantics.
* Use of emojis to better indicate leaf merging in the printed semantics tree.
* Better assert message for adding invisible child semantics nodes.
* Make some semantics tests robuster by not relying on creation order of SemanticsNode ids across test boundaries.

Fixes https://github.com/flutter/flutter/issues/13943.

* Revert "Change github readme links to be served by github (#13929)"

This reverts commit fd516d95.

* Revert " Rename SemanticsFlags to SemanticsFlag (#13994)"

This reverts commit 24e3f705.

* Revert "Make artifact downloading more robust for flaky networks (#13984)"

This reverts commit 4d37e03e.

to align with `SemanticsAction` and other enum-like types.

* First version

* Add a clarifying comment

* Add verify to ZipDecoder.decodeBytes call

* Review comments

* Need OS Error for missing files

* FileSystemException, not OSError.

(untested)

Fixes the last bits of #5759.

This reverts commit 57b4a525.

Fixes https://github.com/flutter/flutter/issues/13972

* Pin url_launcher to 1.0.3

* Commit results of 'bin/flutter update-packages --force-upgrade'

* Added TODO

* Explicitly report CFE output(when using --preview-dart-2)

* Fix test so it looks at errorText

* Fix expected text

Unsubscribe should remove RouteAware for all routes.

* Revert "Revert "Revert "Revert "Update Android sdkmanager for all platforms (#13912)" (#13922)" (#13923)" (#13935)"

This reverts commit f6fae1ce.

In this attempt we try to use SDK's with pre-accepted licenses.

* use SDK with pre-accepted licenses

* update readme

Fixes https://github.com/flutter/flutter/issues/11993