The open source OpenXR runtime

c/util: Extract comp_layer_accum, formerly comp_layer_slot, and reduce coupling. master

The "secret" the implementation is hiding is how calls and layers turn into a single structure. Not a great secret but functionality that is needed. c/util: Use comp_layer_accum in comp_base and derived implmentations. c/util: zero the other swapchains. c/util: Inline two functions. Part-of: <https://gitlab.freedesktop.org/monado/monado/-/merge_requests/2317>