Template Foldability diff view should ignore file paths

[jonwis]

In this view, the first line difference is only in the source file - this DLL pulls in static libs that use the same cppwinrt version, but different runs of its projector, so it's got both lib1/obj/winrt/base.h and lib2/obj/winrt/base.h. The second difference is actually meaningful (comparing IIDs in queryinterface.)

I'd like to fix the diff view to either ignore the file-path difference in the view, or mask the "noncommon source base path" so only the real differences in code are shown.