This pass implements all the implicit conversions required by the
VK_KHR_sampler_ycbcr_conversion specification.

It also inserts plane sources onto sampling instructions that we then
let the pipeline layout pass deal with, when mapping things correctly
to descriptors.

v2: Add new file to meson build (Lionel)
    Use nir_frcp() rather than (1.0f / x) (Jason)
    Reuse nir_tex_instr_dest_size() rather than handwritten one (Jason)
    Return progress (Jason)
    Account for array of samplers (Jason)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>