Add support for rect textures (sampler2DRect)

We can enable lowering for sampler2DRect - it's just a matter of setting lower_rect to true in nir_lower_tex_options in lima_program.c, however we need to add second nir_lower_tex with lower_txs_lod=true.

Beside that we need to implement nir_texop_txs which returns texture size. Panfrost implements it with sysvals which are actually uniforms, we can use the same approach in lima.