libobs: Add UYVA pixel format support

[Lordmau5]

Description

This pull request is heavily based on this one which was recently closed due to inactivity: #10345

For readability reasons I'm going to be copying all of its information into this one, too.

This change adds the YUVA pixel format, which is a 4:2:2:4 semi-planar with packed YUV data in one place and a second plane with only alpha data as documented here: docs.ndi.video/docs/sdk/frame-types
Note that best I can tell, NDI is the only software that uses this pixel format, and other software may use YUVA to refer to a different format. I am open to suggestions of alternative names for this format in OBS.

Motivation and Context

NDI uses an unusual format for pixel data with transparency, and obs-ndi was silently ignoring the alpha plane of that format leading to these bug reports :DistroAV/DistroAV#937 and DistroAV/DistroAV#983

The motivation and context for making a new PR is due to the inactivity on the previous one as well as missing formatting, rebasing and compilation issues.

Additionally, this PR also includes a small oversight in the pixel shader (format_conversion.effect) as well as bringing UYVA support into a 2 more places (OBSBasic.cpp and video-fourcc.c)

How Has This Been Tested?

The original PR has been tested on Windows and macOS using one OBS instance sending a source with transparency over NDI (which already worked correctly) and another instance receiving (along with a small patch to obs-ndi to use the new format which I will submit as a PR on that side after this has been merged)

This PR has been tested only on Windows but with the same approach (small patch to DistroAV, formerly known as obs-ndi)

Types of changes

• New feature (non-breaking change which adds functionality)

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. (<- Unsure how squashing works with co-authoring so I didn't do this yet)
• I have included updates to all appropriate documentation.