nir/from_ssa: Use nir_builder for emit_copy
nir/from_ssa: Use nir_builder for emit_copy

This lets us get rid of the void *mem_ctx parameter and make things a
bit more type safe.

Reviewed-by: Eduardo Lima Mitev <86e6f0c9eba14994f25948ad50c226b324e9fa92@igalia.com>
Reviewed-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler