[clang][lex] Always pass suggested module to `InclusionDirective()` callback (#81061)

This patch provides more information to the
`PPCallbacks::InclusionDirective()` hook. We now always pass the
suggested module, regardless of whether it was actually imported or not.
The extra `bool ModuleImported` parameter then denotes whether the
header `#include` will be automatically translated into import the the
module.

The main change is in `clang/lib/Lex/PPDirectives.cpp`, where we take
care to not modify `SuggestedModule` after it's been populated by
`LookupHeaderIncludeOrImport()`. We now exclusively use the `SM`
(`ModuleToImport`) variable instead, which has been equivalent to
`SuggestedModule` until now. This allows us to use the original
non-modified `SuggestedModule` for the callback itself.

(This patch turns out to be necessary for
https://github.com/apple/llvm-project/pull/8011).