25578 Add more doc for how the plugin registration process works and how to customize it (platform-android, cla: yes, waiting for tree to go green)

25579 Distinguish between touch and mouse input (cla: yes, platform-windows, embedder)

25585 Fix the kernel path in the DartPersistentHandleTest.ClearAfterShutdown test (cla: yes)

25589 Roll Skia from 785a3262d116 to cdee12018087 (13 revisions) (cla: yes, waiting for tree to go green)

25591 Roll Dart SDK from e8cb08ba389a to 05538f0a8a5b (3 revisions) (cla: yes, waiting for tree to go green)