35919 Animation API doc improvments (a: animation, cla: yes, framework, waiting for tree to go green)

35926 Add example showing how to move from one field to the next. (cla: yes, d: api docs, d: examples, framework)

35932 Upgraded framework packages with ‘flutter update-packages –force-upgrade’. (cla: yes, framework)

35941 SliverLayoutBuilder (cla: yes, f: scrolling, framework)

35942 Use test instead of test_api package in platform_channel_swift example tests (a: tests, cla: yes, d: examples, team)

35971 [ImgBot] Optimize images (cla: yes, team)

35979 Optimizes gesture recognizer fixes #35658 (cla: yes, f: gestures, framework)