Auto merge of #24668 - tuncer:configure-media-stack-v2, r=asajeffrey

Allow build to explicitly set the media stack

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_[This is based on @asajeffrey's work in #23423, and is a rebase and continuation of that branch]_

This allows `./mach build` to override the media stack, which is currently hard-wired based on the target. To skip gstreamer, run `./mach build -d --media-stack=dummy`.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23050 (GitHub issue number if applicable)
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- [x] These changes do not require tests because it's build infra

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