46055 v1.12.13+hotfix.2 cherry-picks (cla: yes, engine, framework, team, tool)

46059 Roll engine 3e6d6bc612fd..1cdfc99314df (1 commits) (autoroller: commit, cla: yes)

46081 Update SliverPersistentHeader docs (cla: yes, framework)

46083 Add a VisualDensity manual test (cla: yes, f: material design, framework, team, tool)

46090 Add visual density to the gallery options (cla: yes, d: examples, team, team: gallery)

46091 Add visualDensity to checkbox, radio, icon button, and chip. (cla: yes, f: material design, framework, team)