[Libtaskmanager] Add support for regular expression mapping

This allows more complicated rules, useful for matching Chrome webapps to their
respective desktop file where we need to change crx_foo to chrome-foo-default.

BUG: 358277
CCBUG: 356609
FIXED-IN: 5.7.0

Differential Revision: https://phabricator.kde.org/D1673