dzn: Add support for KHR_shader_draw_parameters
Based on !15911 (merged) (depends on dzn: Use core helpers to fill physical device features/properties).
We are already exposing all draw parameters to shader except the DrawIndex one. Let's fix that by adding a new internal push constant containing this value.
dzn: Fix exec_buf_stride calculation and dzn: Simplify the triangle_fan_rewrite_index shader are not directly related to this feature, but I found those issues while working on draw_parameters, so I thought I'd make it part of the same MR.