80000 [flutter_tools] Allow flutter build aar to know the null safety mode ahead of time (tool, cla: yes)

80002 Migrate more tool unit tests to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

80008 Migrate intellij tests and context_test to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

80011 Cast Config values map values to dynamic instead of Object (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

80016 Migrate template to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)