cmd/compile: support new fully-inst types referenced during inlining

Modify the phase for creating needed function/method instantiations and
modifying functions to use those instantiations, so that the phase is
self-contained and can be called again after inlining. This is to deal
with the issue that inlining may reveal new fully-instantiated types
whose methods must be instantiated.

With this change, we have an extra phase for instantiation after
inlining, to take care of the new fully-instantiated types that have
shown up during inlining. We call inline.InlineCalls() for any new
instantiated functions that are created.

Change-Id: I4ddf0b1907e5f1f7d45891db7876455a99381133
Reviewed-on: https://go-review.googlesource.com/c/go/+/352870


Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Alexander Rakoczy <alex@golang.org>