cmake: Update formatting and switch to native find_package call for Qt6

[PatTheMav]

Description

Updates the CMake build script for the submodule as a companion PR to https://github.com/obsproject/obs-studio/pull/9769.

Motivation and Context

Clean up the code and remove unnecessary build specifics.

The main breaking change of this PR is that it correctly requires the wrapper library to be built according to the official documentation for Windows:

Linking CEF dynamically (as obs-browser does) requires the use of the dynamic MSVC runtime library and also disabling the sandbox functionality.

(Runtime library changes on Windows have been moved to a separate PR).

Current code works around this issue by forcing the runtime library to be linked statically, a workaround which is removed by this PR.

How Has This Been Tested?

Tested on Windows 11 with an updated wrapper library (built according to the documentation).

Types of changes

• 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.

[RytoEX]

IIRC, this looked fine to me. The main caveat is that we would have to rebuild the Windows CEF wrapper to coincide with pulling this update into obs-studio?