[FilteredDirIterator] Avoid RegExp overhead for exact matches
Summary:
Quite a few of the filter strings are exact matches without wildcards,
add an extra QSet for these. This saves about 30% of the runtime cost
of the FilteredDirIterator.
Test Plan: valgrind --tool=callgrind baloo_file
Reviewers: Baloo, ngraham, astippich, poboiko, broulik
Reviewed By: Baloo, ngraham
Subscribers: kde-frameworks-devel
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D21579