Sema: Use getAllMembers() from collectVisibleMemberDecls()
I had to disable typo correction in one test case to get it to pass without
diagnosing a cycle as a result of Sendable checking. But that's OK, because:
- Sendable checking is prone to request cycles and needs to be redesigned
- Typo correction is turned off in production
(cherry picked from commit 89ad597fe3bc4a5846ef54f7dccda2c762c7347c)
