anv: Enable VK_VALVE_mutable_descriptor_type

anv: Enable VK_VALVE_mutable_descriptor_type

This change introduces the anv_descriptor_size_for_mutable_type and
anv_descriptor_data_for_mutable_type helpers to compute the size and
data flags respectively for mutable descriptor types.

In order to make handling these types easier we now store a precomputed
descriptor stride for all types and use in the in appropriate places.

We also need to adjust the compiler to take into account this descriptor
stride. To that extent, we now pack the stride into the upper 16 bits
alongside the index and the dynamic offset index and use it later to
compute the correct offset.

Closes: #4250
Signed-off-by: Rohan Garg <rohan.garg@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14633>