This re-lands the Focus changes in #30040. Correctness changes in routes.dart, and removes the automatic requesting of focus on reparent when there is no current focus, which caused undesirable selections.
Addresses #11344, #1608, #13264, and #1678Fixes#30084Fixes#26704
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 #1678Fixes#30084Fixes#26704
This converts all remaining "## Sample code" segments into snippets, and fixes
the snippet generator to handle multiple snippets in the same dartdoc block
properly.
I also generated, compiled, and ran each of the existing application samples,
and fixed them up to be more useful and/or just run without errors.
This PR fixes these problems with examples:
1. Switching tabs in a snippet now works if there is more than one snippet in
a single dartdoc block.
2. Generation of snippet code now works if there is more than one snippet.
3. Contrast of text and links in the code sample block has been improved to
recommended levels.
4. Added five new snippet templates, including a "freeform" template to make
it possible to show examples that need to change the app instantiation.
5. Fixed several examples to run properly, a couple by adding the "Scaffold"
widget to the template, a couple by just fixing their code.
6. Fixed visual look of some of the samples when they run by placing many
samples inside of a Scaffold.
7. In order to make it easier to run locally, changed the sample analyzer to
remove the contents of the supplied temp directory before running, since
having files that hang around is problematic (only a problem when running
locally with the `--temp` argument).
8. Added a `SampleCheckerException` class, and handle sample checking
exceptions more gracefully.
9. Deprecated the old "## Sample code" designation, and added enforcement for
the deprecation.
10. Removed unnecessary `new` from templates (although they never appeared in
the samples thanks to dartfmt, but still).
Fixes#26398Fixes#27411
