87561 [DOCS]Update some Focus docs (framework, cla: yes, d: api docs, waiting for tree to go green, documentation)

d: api docs - 18 pull request(s)

78173 Improved AssetImage Docs (framework, cla: yes, d: api docs, waiting for tree to go green, documentation)

78284 Add CupertinoScrollbar api docs (framework, cla: yes, f: cupertino, d: api docs, d: examples, waiting for tree to go green, documentation)

81706 Integrate MaterialBanner with the ScaffoldMessenger API (severe: new feature, framework, a: animation, f: material design, a: fidelity, cla: yes, d: api docs, d: examples, a: quality, waiting for tree to go green, documentation)