When SPIRV-Cross encounters a GLSL storage buffer runtime sized array,
it generates MSL code which expects a "buffer size buffer" containing a
list of storage buffer sizes to be bound. This patch adds RHI backend
support for Metal "buffer size buffers" on compute and graphics
(including tessellation) pipelines. Includes unit tests.
An accompanying patch to qtshadertools is required.
Change-Id: I9392bfb21803e1a868d7de420fedc097a8452429
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>