Support regex format include rules in user scripts

For user scripts with `@include` and `@exclude` directives in their
headers, if the value starts and ends with `/` then assume it is a
regular expression to be matched against a URL. This feature has been in
the original greasemonkey module since 2011 and currently in webengine
regex include rules are being blindly passed to the glob matcher.

An alternative to this approach of leaving the bracketing slashes on the
values as a kind of in-band signalling (and making the glob escaping
conditional) would be to add new members to the UserScriptData struct for
holding regex patterns.

This commit also applies cleanly to v5.8 and every release after it.

[ChangeLog][][UserScript] User script metadata parsing now supports regular
expressions in @include and @exclude rules.

Task-number: QTBUG-65484
Change-Id: Ie2e483419f6784f995131ffb7d2d5e91c2c55b1d
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
Reviewed-by: Szabolcs David <davidsz@inf.u-szeged.hu>
Reviewed-by: Florian Bruhin <qt-project.org@the-compiler.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>