Description

This changes cleans up some deprecated functions that were removed in
Qt6. Some are placed behind version ifdefs and others are replaced for
their non-deprecated Qt5 version.

Motivation and Context

There wont be any more Qt5 releases, and the differences to make things compile arnt too different. QtX11Extras and QtMacExtras were removed which complicates making this actually work, but with some creative definitions it compiles enough to test this PR.

How Has This Been Tested?

Compiles against Qt6 and Qt5.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.