62499 fix unresolved doc references in widgets - part 2 (cla: yes, framework, waiting for tree to go green)

62500 Fix todo in restoration framework (cla: yes, framework, waiting for tree to go green)

62509 Fix more unresolved doc references in material (cla: yes, f: material design, framework, waiting for tree to go green)

62513 migrate services to nullsafety (cla: yes, framework, team)

62520 Fix even more unresolved doc references in material (cla: yes, d: api docs, documentation, f: material design, framework, team, waiting for tree to go green)

62552 Add comment to developers about adding new system sound types (cla: yes, framework)