cmake: Move common variables to an inherited preset

[RytoEX]

Description

Move ENABLE_FRONTEND_API and ENABLE_QT from individual presets to a common preset that is hidden but inherited by the individual presets.

Motivation and Context

Generally, these will have the same values on all platforms. Make it easier for plugin devs to enable or disable Frontend API and Qt for all presets/platforms.

Devs can still override this per preset if needed by simply setting a different value in an individual preset.

Fixes #103

How Has This Been Tested?

Haven't tested locally. CI should be able to test.

Types of changes

• Tweak (non-breaking change to improve existing functionality)
• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

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