68553 [gen-l10n] Fix untranslated messages (a: internationalization, cla: yes, team, tool, waiting for tree to go green)

68645 Migrate flutter_localizations to null safety. (a: internationalization, cla: yes, f: cupertino, f: material design, framework, team)

68714 Revert “enable unnecessary_string_escapes and use_raw_strings” (a: internationalization, a: tests, cla: yes, f: cupertino, f: material design, framework, team, tool)

68774 [gen_l10n] Make resource attributes optional for simple cases (a: internationalization, cla: yes, tool)

69016 [gen_l10n] Add base method code comments for improved discoverability (a: internationalization, cla: yes, tool, waiting for tree to go green)