[flutter_plugin_tools] Legacy analysis fails on @docImports of dev dependencies #196406

Legacy analysis (.ci/scripts/analyze_legacy.sh, used by the Linux analyze_legacy N-1 and N-2 tasks in flutter/packages) runs remove-dev-dependencies and then analyze --lib-only. If a package's lib/ code has a @docImport of one of its dev dependencies, that import can't be resolved once the dev dependencies are removed, so analysis fails with uri_does_not_exist_in_doc_import.

Doc imports only affect dartdoc references, not compilation, so this is a false positive for what legacy analysis is meant to check (that client-facing code still analyzes on N-1 and N-2).

This first showed up in flutter/packages#13628: N-1 moved to 3.47.9, so cupertino_ui (which requires Flutter 3.47) is legacy-analyzed for the first time. 20 of its lib/ files have /// @docImport 'package:material_ui/material_ui.dart';, and material_ui is only a dev dependency (because material_ui depends on cupertino_ui). As a workaround, that PR adds // ignore: uri_does_not_exist_in_doc_import (or ignore_for_file) to those files.

Possible fixes:

• Don't treat uri_does_not_exist_in_doc_import as an error in legacy analysis.
• Have remove-dev-dependencies also remove @docImports of the packages it removes.

Once this is fixed, the ignores in packages/cupertino_ui/lib/ can be removed.