Deps: Bump FFmpeg to 9.0.1

[kamfretoz]

Description of Changes

This PR bumps our ffmpeg version to 9.0.1, as well as:

• Purged the in-tree ffmpeg headers now that we bundled ffmpeg ourselves
• Switch the uses of pix_fmts to avcodec_get_supported_config() since ffmpeg 9 removed it.
• And changes the ffmpeg's dll copy path to not be hardcoded.

Rationale behind Changes

More up-to-date deps the better!

Suggested Testing Steps

Test ffmpeg and that all its codecs still works.

Did you use AI to help find, test, or implement this issue or feature?

Narhp.

[TellowKrinkle]

Is the change backwards compatible with older ffmpeg? If so, you should move the commit that fixes ffmpeg 9 support before the one that enables ffmpeg 9, so you don't have commits that don't build. Same with the "don't hardcode dll path" commit, if that's compatible with both 8 and 9, it should go before the update.

If not, we should probably add an ifdef to allow backwards compatibility, at least for a few ffmpeg versions.

Also, "deprecate" is something a library does. (It's when you mark something you're planning on removing in the future so that users of the library can switch off of it slowly instead of their code breaking right away.) As the user of the library, we can stop using deprecated features, but naming a commit "deprecate <thing>" is really confusing. Who are we keeping it around for? The only user of PCSX2 code is ourselves...

[TheLastRar]

Is the change backwards compatible with older ffmpeg? If so, you should move the commit that fixes ffmpeg 9 support before the one that enables ffmpeg 9, so you don't have commits that don't build. Same with the "don't hardcode dll path" commit, if that's compatible with both 8 and 9, it should go before the update.

Looks like at least avcodec_get_supported_config is supported in 7.1, but not 7.0 ffmpeg github.
I did, however, not test building against 7.1, or 8.X.

[Mrlinkwii]

will probably need to move this to 9.0.1 since that was released

[kamfretoz]

Alright i have re-arranged the commits so the version bumps comes later after the fixes, also renamed the wording of the commit name, and bumped ffmpeg to 9.0.1