If the user wants to indent with tabs, then consider that when adding
source files via the UI. But try not to mix: If the respective variable
already uses a different indentation consistently, then keep using that
one.
Fixes: QTCREATORBUG-8016
Change-Id: I037c9ac4d4e7fbbe5753a846e57d938bbb440d6a
Reviewed-by: David Schulz <david.schulz@qt.io>