agx: Handle loop { if { loop { .. } } }

We need to push loop nesting to handle this correctly -- at the end of the innermost loop, the correct nesting is 1 (from the if), not 0.

Fixes assertion failure in

dEQP-GLES2.functional.shaders.struct.local.dynamic_loop_nested_struct_array_fragment,UnexpectedPass dEQP-GLES2.functional.shaders.struct.local.dynamic_loop_nested_struct_array_vertex,UnexpectedPass dEQP-GLES2.functional.shaders.struct.uniform.dynamic_loop_nested_struct_array_fragment,UnexpectedPass dEQP-GLES2.functional.shaders.struct.uniform.dynamic_loop_nested_struct_array_vertex,UnexpectedPass

Signed-off-by: Alyssa Rosenzweig alyssa@rosenzweig.io