scripts : add Jinja tester PySide6 simple app (#15756)

* feat: add Jinja tester PySide6 simple app

* Linter fixes

* Pylint fixes

* Whitespace

* Add commandline support; add formatter; add extensions

* Remove testing actions

* Silence flake8 warnings for commandline mode

* Apply suggestions from code review

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Fix trailing whitespace/newline logic

* Update scripts/jinja/jinja-tester.py

Co-authored-by: Sigbjørn Skjæret <[email protected]>

* Update scripts/jinja/jinja-tester.py

Co-authored-by: Sigbjørn Skjæret <[email protected]>

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Co-authored-by: Sigbjørn Skjæret <[email protected]>

Author: pwilkin