PySide6 Handle QRegExp case sensitivity, FixedString, and Wildcard pattern syntaxes

[jonahjnewton]

ISSUE: The current tk_core releases do not properly handle case sensitivity in the way apps intend in PySide6. Eg. tk-multi-workfiles2 uses QtCore.Qt.CaseInsensitive to flag that a QRegExp should be case insensitive
https://github.com/shotgunsoftware/tk-multi-workfiles2/blob/3e56df0ce651a814e19fc221a3eda09964a4311e/python/tk_multi_workfiles/entity_tree/entity_tree_form.py#L531

SOLUTION: Recognise QtCore.Qt.CaseInsensitive in the QRegExp to QRegularExpression patcher. Also add pattern syntax handling of FixedString using QRegularExpression.escape() to properly match plain strings and Wildcard using QRegularExpression.wildcardToRegularExpression to properly expand wildcards ininit`.

These changes were made as part of my work at Flying Bark Productions, which my leadership @diegogarciahuerta has generously allowed me to contribute here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.50%. Comparing base (5bfcaa7) to head (41f5f9c).
⚠️ Report is 33 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1075      +/-   ##
==========================================
- Coverage   79.79%   73.50%   -6.30%     
==========================================
  Files         198      198              
  Lines       20776    20623     -153     
==========================================
- Hits        16579    15159    -1420     
- Misses       4197     5464    +1267     

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