[pointer_interceptor] fix integration test (flutter#1675)

[go_router_builder] Readme fixes (flutter#1659)

[go_router]Add pkg:go_router_builder (flutter#1551)

Make corresponding changes to pkg:go_router

Fixes flutter/flutter#99127

Co-authored-by: chunhtai <[email protected]>

[go_router]Add pkg:go_router_builder (flutter#1551)

Make corresponding changes to pkg:go_router

Fixes flutter/flutter#99127

Co-authored-by: chunhtai <[email protected]>

[pigeon] added AST validation phase for generators (flutter#1548)

* [pigeon] added AST validation phase for generators

* added negative test

* updated docstring

[pigeon] Minor fixes to NNBD type handling in Dart (flutter#1543)

[pigeon] Enable NNBD in tool (flutter#1532)

Opts Pigeon into running in NNBD mode. All of the code had already been converted.

Also updates a legacy Dart command (dart pub run) in the test script to the modern version.

Document how to suggest lints for flutter_lints (flutter#1546)

[flutter_markdown] update `markdown` dependency (flutter#1395)

[pigeon] Remove support for non-NNBD (flutter#1524)

Makes a breaking change to remove non-NNBD support, since it adds complexity
to the generator and there's no compelling reason to continue supporting it going
forward.

Also updates some legacy Dart commands in scripts (dartanalyzer, dart pub run)
to their modern versions.