optimizer: simplify inlining algorithm (#47207)

The main purpose of this commit is to try to simplify our inlining
algorithm by removing the delayed callee resolving mechanism (i.e.
`DelayedInliningSpec` stuff), since that kind of mechanism currently
has no users and we provide more fine grained control with
`inlining_policy` now.

This commit also adds some more cleanups, changing argument ordering of
some subroutines so that they are aligned with the other ones, and
removing dead subroutines.