Fix broken framework documentation

Various issues here, but the most recurring one is referencing SystemApi
from public javadoc. Remove or rewrite such references.

Also common is trying to @link IntDefs. Usually this is not necessary,
as the presence of IntDef in the @param/@return auto-generates relevant
documentation.

Bug: 303184203
Test: m docs
Change-Id: Ie59e61881c45c73fbbe08250493bd35eca268ef6