Backport libplacebo compatibility changes from VLC v4

Bumps minimum ver (as on master) and removes the very old/unused tone mapping API. This unfortunately removes most of the ability for users to configure the specifics of the tone-mapping in VLC v3, VLC v4 is required for that. But this should still end up using fallback paths that are "good enough" in terms of quality. Anything better would require access to pl_opengl-backed textures, and backporting that from VLC v4 would be a nightmare.

So, if users are unhappy with the quality, they simply need to update.