gl-renderer: FBO renderbuffer and DMA-BUF import
This is split out from !578 (merged) and allows the GL renderer to render via FBOs instead of using pbuffers, which only work with the surfaceless EGL platform, as well as render into dmabuf renderbuffers imported from the backend.
Basic FBO support is since split out into !1106 (merged), which this MR is now based on.
This is a prerequisite for multi-backend PipeWire support when using the GL renderer.
Edited by Philipp Zabel