`GlesRenderer::cleanup()` not called implictly if GPU is used to import client buffers, but not to render

[ids1024]

https://docs.rs/smithay/0.6.0/smithay/backend/renderer/trait.Renderer.html#method.cleanup_texture_cache notes that this is done implicitly on finishing a Frame.

But if a GPU is used to import dmabufs, but not for rendering, things like cpu_copy() allocate resources, but are never automatically cleanup up.

Smithay should either make sure cleanup occurs automatically in this use case, or document the need to call cleanup_texture_cache.

https://github.com/pop-os/cosmic-comp/pull/1442 is an example of a compositor change for this.