Use Wrapland's new ShmImage class to unpack shared memory Gl subimages
This MR adapts to the Wrapland change in wrapland!71 (merged) and uses it to unpack Gl subimages for shared memory buffers.
When running weston-presentation-shm I saw performance improvements. To improve upon this also the compositing delay timer was reworked to be more conservative about delaying by taking the maximum paint duration from the last 200 frames as a base line.
Closes #64 (closed)
Pipeline won't pass until the Wrapland change is merged.
Edited by Roman Gilg