[NewPM][Inliner] Move the 'always inliner' case in the same CGSCC pass as 'regular' inliner

Expanding from D94808 - we ensure the same InlineAdvisor is used by both
InlinerPass instances. The notion of mandatory inlining is moved into
the core InlineAdvisor: advisors anyway have to handle that case, so
this change also factors out that a bit better.

Differential Revision: https://reviews.llvm.org/D94825