AnalysisOptionsMigration ignores include:, repeatedly rewriting analysis_options.yaml files that already inherit the exclusions #191056

Steps to reproduce

AnalysisOptionsMigration (added in #187940, shipped in 3.47.0) decides whether a project needs migrating by reading only the literal contents of that project's own analysis_options.yaml. It never resolves include:, so a project that already inherits the exclusions from a shared analysis options file gets rewritten anyway, on every command that calls ensureReadyForPlatformSpecificTooling (flutter pub get, flutter analyze, flutter run, flutter build).

From a stock flutter create repro:

1. Move the analyzer config into repro/shared_options.yaml:

   include: package:flutter_lints/flutter.yaml
   
   analyzer:
     exclude:
       - build/**
       - android/**
       - ios/**
       - web/**
       - windows/**
       - macos/**
       - linux/**

2. Reduce repro/analysis_options.yaml to include: shared_options.yaml
3. Confirm the inherited exclusions really are in effect. dart analyze doesn't run the migration, so it sees the unmodified file:

   $ printf 'int probe() => "nope";\n' > android/probe.dart && dart analyze
   No issues found!
   
   $ printf 'int probe() => "nope";\n' > lib/probe.dart && dart analyze
     error - lib/probe.dart:1:16 - A value of type 'String' can't be returned ... - return_of_invalid_type

   android/ is excluded, lib/ is still analyzed. The shared config works.
4. flutter analyze

Expected results

No migration. The project already excludes every directory in excludesToExclude.

Actual results

$ flutter analyze
Upgrading analysis_options.yaml to exclude build and platform directories.

The file is rewritten to re-add the seven exclusions locally, duplicating what the included file already provides. Reverting and re-running any Flutter command adds them straight back, so there's no way to keep the config centralized.

This hurts monorepos with a shared lints package. supabase/supabase-flutter publishes a supabase_lints package that all 20 workspace packages include; putting the exclusions there analyzes correctly, but flutter pub get still rewrites all 20 files, so a routine pub get leaves every contributor with a 20-file dirty working tree.

Suggested fix

analysis_options_migration.dart#L50-L65 inspects root['analyzer']['exclude'] directly after loadYamlNode. Resolving include: (relative paths and package: URIs) before computing needsMigration would make it a no-op whenever the effective options already carry the exclusions, whichever file in the chain declares them.

If full include resolution is too costly for a path that runs on every command, a narrower fix would be to skip the migration when the local file is only an include: directive, or to add an opt-out flag.

Flutter Doctor output

[✓] Flutter (Channel stable, 3.47.0, on macOS 26.6.1 25G76 darwin-arm64, locale en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0)
[!] Xcode - develop for iOS and macOS
    ✗ Xcode installation is incomplete; a full installation is necessary for iOS and macOS development.
    ! CocoaPods not installed.
[✓] Chrome - develop for the web
[✓] Connected device (2 available)
[✓] Network resources