[Attributor] Cleanup manifest and liveness for CGSCC passes

There was some ad-hoc handling of liveness and manifest to avoid
breaking CGSCC guarantees. Things always slipped through though.
This cleanup will:

1) Prevent us from manifesting any "information" outside the CGSCC.
   This might be too conservative but we need to opt-in to annotation
   not try to avoid some problematic ones.
2) Avoid running any liveness analysis outside the CGSCC. We did have
   some AAIsDeadFunction handling to this end but we need this for all
   AAIsDead classes. The reason is that AAIsDead information is only
   correct if we actually manifest it, since we don't (see point 1) we
   cannot actually derive/use it at all. We are currently trying to
   avoid running any AA updates outside the CGSCC but that seems to
   impact things quite a bit.
3) Assert, don't check, that our modifications (during cleanup) modifies
   only CGSCC functions.

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