18350 Roll src/third_party/skia 056d543c91e0..71903997254f (7 commits) (cla: yes, waiting for tree to go green)

18351 null-annotate compositing.dart (cla: yes)

18352 null-annotate lib/ui/isolate_name_server.dart (cla: yes)

18353 null-annotate lib/ui/plugins.dart (cla: yes)

18354 null-annotate lib/ui/pointer.dart (cla: yes)

18356 sync ui geometry.dart into web_ui geometry.dart; add null safety annotations (cla: yes)

18359 Rename NULL tests to Nullptr for consistency (cla: yes)