28139 fuchsia: Improve FakeSession & add tests (affects: tests, cla: yes, waiting for tree to go green, platform-fuchsia, tech-debt)

28142 Roll Dart SDK from 17c9a00cce20 to fecde133832e (1 revision) (cla: yes, waiting for tree to go green)

28143 Revert “[ci.yaml] Promote roller to blocking” (cla: yes, waiting for tree to go green)

28145 Roll Skia from 957ed75731e0 to 7020699e3835 (7 revisions) (cla: yes, waiting for tree to go green)

28146 Fix Libtxt unit test errors found by ASAN (cla: yes, waiting for tree to go green)