Reimplement ping-pong animation and reverse playback

[TokageItLab]

This is a resend of #48332.

Once approved before, but temporarily reverted due to conflicts with a huge overhaul of the animation features.

Until that overhaul is finished, it will be left as a draft PR to check and resolve conflicts.

Bugsquad edit: Fixes #50636. Fixes #54619. Supersedes #51576.

[mhilbrunner]

Seems that overhaul has largely finished, just FYI :)

[fire]

Ah it's not ready yet, I was pinged.

[TokageItLab]

@reduz @fire Rebased. I did a quick test using a previous project but Blendshape and compressed tracks were not tested (for some reason, the mesh instance with Blendshape crashes, and I don't know much about compression tracks in terms of how they are generated), but I believe that the code seems to be fine.

ping-pong_demo_re.zip

[akien-mga]

Thanks!

[magian1127]

Can fix the bug of 3.X?

[TokageItLab]

We need to cherry-pick #51576 to fix #50636 and #54619. Ping @timothyqiu.

[timothyqiu]

Ah, I tested those issues and they were resolved by this PR. I thought this would be backported... Should I reopen my PR?

[TokageItLab]

This PR is large, so it is difficult to backport it. In particular, loop_mode has been changed the type bool to int, so it is incompatible and old animation file needs to be migrated. I think it is better to leave it to the 4.x migrator than to lose compatibility within 3.x.

So, smaller fixes should be cherry-picked separately for 3.x.