libobs: Include all audio priming packets if closest is start

[derrod]

Description

If the audio packet chosen for A/V sync is the start of the encoded bitstream also include all previous audio packets to ensure all "priming" samples are included.

Motivation and Context

Same as #10689 but will ensure that all priming samples for AAC are included (2 additional packets for CoreAudio, 1 additional packet for FFmpeg). This may however require some further testing and thought to ensure multi-track audio/video does not cause issues.

How Has This Been Tested?

Did some test recordings and looked at the results in Resolve.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

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.