obs-text: Fix changing fonts for Qt 6.7+

[RytoEX]

Description

Add support for variable font weights to obs-text (the GDI+ Text Source).

Instead of simply checking if a font is bold or not (which in Qt is equivalent to font.weight() > Medium / font.weight() > 500),

Motivation and Context

Fixes #12393

https://doc.qt.io/qt-6.8/qfont.html#Weight-enum
https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-logfontw

How Has This Been Tested?

Tested locally on Windows 11.

For the most part, this improves user experience when using variable fonts. Some changes, such as between Regular and Medium styles, still do not seem to show a difference, even if the code does not actually call UpdateFont().

Types of changes

• Bug fix (non-breaking change which fixes an issue)

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.

[RytoEX]

Will dig into this a bit more. It seems the QFont isn't fully initialized until after QFontDialog returns, and I'll have to determine if we need to deal with the font weight at all in the properties-view.

[Lain-B]

Outside of the build issues this seems fine 👍