Inliner: initial version of SizePolicy

Inliner: initial version of SizePolicy

Add a new inline policy that tries to inline as much as possible
without increasing method size.

Fix one test that had an expected inline that doesn't happen under
the SizePolicy, by marking a method with AggressiveInline.

Commit migrated from https://github.com/dotnet/coreclr/commit/f57f3737a356f12fb494945c5750980fe14af020