As all the .ui files follow a set schema, providing a way to validate
that schema is useful for manual XML modifications.
XML-Schema-Qt5.15.xsd source: https://doc.qt.io/qt-5/designer-ui-file-format.html
Note: some lines had to be commented out as they are not valid in XSD.
When a new version of Qt is used, compare the diff and update as necessary.
This file doesn't do anything on its own, but can be paired with an IDE
or a standalone linter to perform validation.
