compiler: add a vs.tes_agx bit

So we can distinguish lowered tess eval shaders masquerading as hardware vertex
shaders from actual software vertex shaders, for determining what stage to pull
descriptors.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27616>

src/compiler/shader_info.h

@@ -389,6 +389,9 @@ typedef struct shader_info {
           */
          uint8_t blit_sgprs_amd:4;
 
+         /* Software TES executing as HW VS */
+         bool tes_agx:1;
+
          /* True if the shader writes position in window space coordinates pre-transform */
          bool window_space_position:1;