Add support for explicit synchronization, take 3

The protocol lives in !4262 (merged), and this MR contains the wlroots renderer/backend changes.

• Consider dropping the example
• Consider including the acquire timeline in wlr_buffer?
• Instead of passing timelines to wait on when rendering a texture, add a new render pass function to wait for a timeline? (Or pass a list of timelines to wait on) (!4260 (comment 2394975))

Follow-up work:

• Multi-GPU support
• Vulkan renderer support
• libliftoff interface support
• Handle out-of-order signalling for swapchain buffers
• Pass IN_FENCE_FD for cursor plane and output layers (#3880)
• Fine-grained release points (#3881)
• Add support for EGL_EXT_image_implicit_sync_control (#3882)

Sway patch: https://github.com/swaywm/sway/pull/8156