SelectableText defers to EditableText for wantKeepAlive, plus improved docs.

This reverts commit 988959da.

This reverts commit 9412edf1.

This reverts commit 0eeb026e.

For https://github.com/flutter/flutter/issues/91625

@blasten @GaryQian

* 9b200e156 Roll Dart SDK from 9f61c2487bbd to 3a963ff14181 (7 revisions) (flutter/engine#30011)

* fada03555 Use WindowInfoTracker.Companion.getOrCreate instead of the short version (flutter/engine#30012)

* d28047579 Non painting platform views (flutter/engine#30003)

* b420c1646 [macOS] MacOS Keyboard properly handles multi-char characters (flutter/engine#30005)

* 0a6098bcf [Win32, keyboard] Fix dead key events that don't have the dead key mask (flutter/engine#30004)

* 8ac9366c7 Fix sceneElement analysis error (flutter/engine#30038)

* 5ad06c213 Share the io_manager between parent and spawn engine (flutter/engine#29915)

* 69be405e8 Run Dart VM tasks on the engine's ConcurrentMessageLoop instead the VM's separate thread pool. (flutter/engine#29819)

* c85a129b4 Roll Dart SDK from 3a963ff14181 to 8bb2e56ec900 (4 revisions) (flutter/engine#30045)

* abf6c34ea Eliminate hardcoded scale factor in a11y scroll (flutter/engine#30013)

* d184d9b45 Roll Skia from fa183572bfd3 to d3399178196e (17 revisions) (flutter/engine#30047)

* 476ed30dd Roll web_installers simulators package (flutter/engine#30035)

* 62113c4f5 Revert dart to 9f61c2487bbd (flutter/engine#30056)