[FilteredDirIterator] Combine all suffixes into one large RegExp

Summary:
Most of the about 50 default filters are suffix matches, which can be
easily combined into one large regular expression. Doing so reduces
the matching cost by about 80%.

Test Plan: valgrind --tool=callgrind baloo_file

Reviewers: Baloo, ngraham, poboiko

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D21583