plugins: Move AMF encoders from obs-ffmpeg as a separate plugin

[tytan652]

Description

Move AMF encoders from obs-ffmpeg as a separate plugin.

Motivation and Context

AMD encoder implementation does not rely on FFmpeg.

How Has This Been Tested?

No code change, checking and testing Windows artifacts was not done.

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.

[WizardCM]

Friendly reminder: translations will need to be moved/duplicated from the previous plugin.

[Ryu0833]

amf-test change the cmake folder targt from obs-ffmpeg to obs-amf