78975 [gen-l10n] Remove more ignores, conditionally generate some code (a: internationalization, cla: yes, tool, waiting for tree to go green)

79263 [gen-l10n] Add nullable-getter flag (a: internationalization, cla: yes, tool, waiting for tree to go green)

79460 [Stocks App] NNBD migration, refresh gen-l10n (a: internationalization, a: null-safety, cla: yes, team, waiting for tree to go green)

d: api docs - 13 pull request(s)

74415 Adding hero example (cla: yes, d: api docs, d: examples, documentation, framework, waiting for tree to go green)