Switch to upstream plume.

[squidbus]

• Add plume submodule pointing upstream and remove submodules only used (and already included) by plume.
• Move SDL_VULKAN_ENABLED out to top-level so it can be picked up by both UnleashedRecomp and plume.
• Update for plume changes upstream:
  • No more waitIdle; incorporates changes from Remove the need for vkDeviceWaitIdle. #1364 to adapt.
  • RenderTextureCopyLocation::Subresource takes separate mip level and array slice rather than combined subresource index.
  • macOS support takes Cocoa window handle rather than SDL window.

Have personally tested this on Windows (D3D12 and Vulkan) and macOS (Vulkan).

CI build: https://github.com/squidbus/UnleashedRecomp/actions/runs/16706866279