Backport analyzer 12 support for gql codegen stable

[knaeckeKami]

Summary

• backport analyzer 12.x support to the stable gql_code_builder line by releasing gql_code_builder 0.13.4
• backport analyzer 12.x support to the stable gql_build line by releasing gql_build 0.13.3
• move the stable gql_build line to dart_style 3.1.8, which requires Dart 3.10+

Testing

• temp stable worktree gql_code_builder: forced analyzer 12.1.0 via pubspec_overrides.yaml; dart analyze succeeded (one pre-existing deprecation info) and dart test passed
• temp stable worktree end_to_end_test_tristate: path-overridden local gql_build/gql_code_builder, forced analyzer 12.1.0; dart run build_runner build --delete-conflicting-outputs && dart test passed under Dart 3.11 with dart_style 3.1.8
• branch codegen/gql_build: dart analyze passes with the updated metadata on Dart 3.11

Notes

• gql_code_builder itself does not need a Dart SDK floor bump for analyzer 12
• gql_build now effectively requires Dart 3.10+ because dart_style 3.1.8 is the first formatter release that works with analyzer 12