[Mesa-dev] RFC - shared shader info (Part 1)

[Timothy Arceri]

Having these fields directly in nir_shader makes things difficult for
the shader cache. This series creates a shared shader info and makes a
start at the large amount of clean-ups this will enable.

I decided to send this before getting too carried away to make sure
people are happy with this change. If everyones happy I'll start work
on part 2.