rather than resolving them once in bulk (for the code model) and once
per pri file (for the project view), resolve them only in bulk, but
"tag" them. then do a cheap filtering pass for the project view.

as a side effect, this fixes the problem that sources that are listed by
a file that is not shown in the project tree (as is the case for qrc
files synthesized by resources.prf) would not be shown at all. instead,
these sources now appear belonging directly to the pro file.

Task-number: QTCREATORBUG-3670
Change-Id: I1a1756d95bd90db4da1274eebcc4dad2a854f43d
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>