This makes ephemeral symlinks to each plugin, for use by build systems.
This is similar to the logic implemented in the Podfile on iOS and
macOS, but managed internally to the Flutter tool.

Exploration for addressing #32719 and #32720
Related to #41146

This re-lands #49235 with the addition of includeSemantics flag on the Focus widget so that the FocusTraversalGroup can create a Focus widget without affecting the semantics tree.

The FocusTraversalGroup uses the Focus widget to create a grouping of descendants for traversal, but doesn't actually participate in focus (canRequestFocus is always false), so we don't want it to add a Semantics widget in that case, since that can cause semantics changes. The canRequestFocus attribute can also be used when a widget is disabled, so we do sometimes want to include Semantics even if that is false, but not in the case where it is always false, as for FocusTraversalGroup.

- Added a test to make sure that FocusTraversalGroup doesn't add any semantics information.

This fixes a problem when unfocusing focus nodes where the ancestor focus nodes and scopes don't receive notification that a child was unfocused.

Fixes #43497

* f49a8b62f Roll src/third_party/skia c03e6982f96f..465864cad5d2 (14 commits) (flutter/engine#16524)

* c477c0644 Enable verbose logging for shell unittests on Fuchsia (flutter/engine#16526)

* a662579f7 Clear frame references at the end of every CanvasKit frame (flutter/engine#16525)

* 3f31ea3d3 Roll src/third_party/skia 465864cad5d2..21f382c19d76 (6 commits) (flutter/engine#16528)

* 38fb6b135 Roll fuchsia/sdk/core/linux-amd64 from 8L7NY... to Bmq1m... (flutter/engine#16529)

* 9c0168a5a Roll fuchsia/sdk/core/mac-amd64 from PMcw3... to 7JkB7... (flutter/engine#16530)

* e8a888dfa Roll src/third_party/skia 21f382c19d76..f83d0346c06a (2 commits) (flutter/engine#16532)

* 1e8b33130 Roll src/third_party/dart 5244d99a5d4e..5fc031ebc1d7 (42 commits) (flutter/engine#16533)

* c4e3ae6ae Roll src/third_party/skia f83d0346c06a..88c3793a4eaa (1 commits) (flutter/engine#16534)

* 6cdb14e17 Roll src/third_party/skia 88c3793a4eaa..abefc9c170c9 (1 commits) (flutter/engine#16535)

* 975acd8ff Roll src/third_party/skia abefc9c170c9..4fe89b4d871d (2 commits) (flutter/engine#16536)

* b7424d0ce Roll src/third_party/dart 5fc031ebc1d7..30151a654151 (2 commits) (flutter/engine#16537)

* 25e812778 Roll src/third_party/skia 4fe89b4d871d..dc2782c380f6 (1 commits) (flutter/engine#16538)

* 74fa10c95 Roll src/third_party/dart 30151a654151..76b18c455e2c (1 commits) (flutter/engine#16539)

* 91b8e406c Roll src/third_party/skia dc2782c380f6..cdf2491afa04 (1 commits) (flutter/engine#16540)

* 5acf9b195 Roll src/third_party/skia cdf2491afa04..50a490a1a4fb (2 commits) (flutter/engine#16541)

* 989777718 Roll src/third_party/skia 50a490a1a4fb..c3b67eb988c8 (4 commits) (flutter/engine#16542)

* 78a890972 Use os_log instead of syslog on Apple platforms (flutter/engine#13487)

* ea56ad22d libtxt: use a fixture in the benchmarks (flutter/engine#16531)

* a61dbf2f6 Revert "Use os_log instead of syslog on Apple platforms (#13487)" (flutter/engine#16546)

* 539f64f56 [fuchsia] Disable retained layers (flutter/engine#16548)

* c3b507248 Expose DPI helper functions for Runner apps to use (flutter/engine#16313)

* 5041ff1b1 support endless trace buffer (flutter/engine#16520)

* 6aacf5e76 Re-land: Use os_log instead of syslog on Apple platforms (flutter/engine#16549)

* a5736b85d Roll src/third_party/skia c3b67eb988c8..b1525c721ea6 (4 commits) (flutter/engine#16543)

* 49a370f8e Roll src/third_party/dart 76b18c455e2c..e4c39721c473 (6 commits) (flutter/engine#16544)

* 270421c10 Fix ensureInitializationCompleteAsync callback when already initialized. (#39675) (flutter/engine#16503)

* ca02b9197 Prevent long flash when switching to Flutter app. (#47903) (flutter/engine#16527)

* 44e80fd61 skiping tests in Safari. LUCI recipe for Mac is ready. this is the only step left for stopping us running unit tests in Safari (flutter/engine#16550)

* 5fb0116d6 iOS platform view gesture blocking policy. (flutter/engine#15940)

* e0ebaea59 Revert "Re-land: Use os_log instead of syslog on Apple platforms (#16549)" (flutter/engine#16558)

Revert "AlertDialog.actionsOverflowButtonSpacing and ButtonBar.overflowButtonSpacing (#50609)" (#50674)

* Add ButtonBar.overflowButtonSpacing

* Add AlertDialog overflow button spacing functionality

This reverts commit 8ef5e2f0 because it breaks some semantics tests.

* a195a92cc [SkParagraph] Text layout benchmarks using SkParagraph (flutter/engine#16373)

* 0340d457a Roll fuchsia/sdk/core/mac-amd64 from fvWgE... to FLFOw... (flutter/engine#16498)

* 9443518f6 Fix safe area reporting with transparent FlutterActivitys. (#46060) (flutter/engine#16208)

* 0980b2ad5 Roll src/third_party/skia 9f3eef796f63..b2031d4255e2 (12 commits) (flutter/engine#16499)

* 8f03a563d Check Java formatting in format.sh (flutter/engine#16500)

* 077918dcf Apply Google Java format (flutter/engine#16501)

* ec1b2e39f Roll src/third_party/skia b2031d4255e2..a9405c2a2967 (5 commits) (flutter/engine#16502)

* 82d193241 Roll src/third_party/skia a9405c2a2967..8dad1ffd81f8 (1 commits) (flutter/engine#16505)

* a302bfd06 Roll src/third_party/dart fd992e423ef6..4310f50edc95 (17 commits) (flutter/engine#16506)

* a86f4cba3 Roll fuchsia/sdk/core/linux-amd64 from LvSlH... to 8L7NY... (flutter/engine#16508)

* 6c04a6960 Roll src/third_party/skia 8dad1ffd81f8..c03e6982f96f (2 commits) (flutter/engine#16510)

* b1aaec3c4 Roll src/third_party/dart 4310f50edc95..9464eb51f539 (2 commits) (flutter/engine#16511)

* cab49e420 Roll fuchsia/sdk/core/mac-amd64 from FLFOw... to PMcw3... (flutter/engine#16512)

* 695a2768e Roll src/third_party/dart 9464eb51f539..f120417ddbfc (1 commits) (flutter/engine#16513)

* 6d3e2606e Roll src/third_party/dart f120417ddbfc..b158bf7bd537 (2 commits) (flutter/engine#16514)

* acc26a2f1 Use Skia to determine "actual" font name in CanvasKit backend (flutter/engine#16504)

* 1daba5318 Partially fix canvas vs text paint order when running on Blink/Webkit browsers (flutter/engine#16483)

* 826b2d46e Apply lints from internal roll (flutter/engine#16509)

* d107eaaa0 Remove mirrors on the web (flutter/engine#16516)

* 7e869faf5 Adds new route annoucement method. (flutter/engine#16523)

* 0e8ed2715 Roll src/third_party/dart b158bf7bd537..5244d99a5d4e (1 commits) (flutter/engine#16517)

This reverts commit 0a38f29c.

Revert "Revert "Reduced code duplication in ink_splash.dart, ink_ripple.dart (#49480)" (#50502)" (#50512)

This reverts commit 9bc0e6a9.