Bug 1930932 [wpt PR 49140] - Add some Media Capabilities API tests, a=testonly

Automatic update from web-platform-tests
Add some Media Capabilities API tests (#49140)

* Add some Media Capabilities API tests

Per spec draft at https://www.w3.org/TR/2024/WD-media-capabilities-20241007/

- Test for 'does not imply a codec'
- Test for 'valid MIME type string'
- Test for 'single media codec'

* Add encodingInfo tests

* Fixed mediaCapabilities.decodingInfo() test case
--

wpt-commits: d3d219eab4b76b6267068837293a1beba002e7d1
wpt-pr: 49140

UltraBlame original commit: ef9e87cd29344b7d91eac77df90869ab0739fb8a

Author: marco-c