49334 refactor generateString to emit simpler dart code (a: internationalization, cla: yes, f: cupertino, f: material design, team, waiting for tree to go green)

49341 fix R8 error message (cla: yes, tool, waiting for tree to go green)

49352 remove unnecessary string interpolations (a: accessibility, a: internationalization, a: tests, cla: yes, d: examples, f: material design, framework, team, team: gallery, tool, waiting for tree to go green)

49357 Update gen_l10n handling of plurals, numbers, and dates (a: internationalization, cla: yes, team, waiting for tree to go green)

49364 Disable flaky LineMetrics test (cla: yes, framework)