nir: Add an option for lowering TessLevelInner/Outer to vecs

The GLSL to NIR compiler supports the LowerTessLevel flag to convert
gl_TessLevelInner/Outer from their GLSL declarations as arrays of
floats to vec4/vec2s to better match how they are represented in
hardware.

This commit adds the similar support to the SPIR-V to NIR compiler so
turnip can use the same IR3/NIR tess lowering passes as freedreno.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5059>
2 files changed