[tool_tests] Remove bringup from Windows tool_tests_commands_2_2 (#191732)

Fixes Windows-specific path and test failures in `tool_tests_commands`
subshard `2_2`:

- Use `Glob(entry).matches(relativePath)` with POSIX relative paths in
`project.dart`.
- Normalize backslashes to POSIX forward slashes in
`SwiftPackagePackageDependency.format()` in `swift_packages.dart`.
- Normalize path separators when encoding `workspacePackages`
dependencies in `preview_pubspec_builder.dart`.
- Consolidate `Cache.disableLocking()` in `upgrade_test.dart`
`setUpAll()` and pass missing `runInContext` overrides.
- Guard NDK directory listing with `ndkDir.existsSync()` in
`build_aar_test.dart`.
- Update test expectations and add retry backoff in
`widget_preview_test.dart`, `test_test.dart`, and
`regress_176018_test.dart`.
- Remove `bringup: true` from `Windows tool_tests_commands_2_2` in
`.ci.yaml`.