Port QRegExp to QRegularExpression

Summary:
Port QRegExp::exactMatch() with QRegularExpression::anchoredPattern().
Port QRegExp::Wildcard with QRegularExpression::wildcardToRegularExpression().
Note that QRegularExpression::wildcardToRegularExpression() returns an anchored
pattern.

Test Plan:
Using the filter bar in dolphin works as before.

All unit tests pass, except:
- kfileitemmodeltest (which is unrelated AFAICS); it fails on master too
- placesitemmodeltest, which fails on master too

Reviewers: #dolphin, elvisangelaccio, meven

Reviewed By: #dolphin, elvisangelaccio

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D26215