Split texture rendering out of wlr_render_pass and introduce a
dedicated wlr_render_texture_pass interface.
Remove the add_texture hook from wlr_render_pass_impl and route
texture rendering through renderer->texture_pass instead.
Split rectangle rendering out of wlr_render_pass and add a dedicated
wlr_render_rect_pass interface.
Remove the add_rect hook from wlr_render_pass_impl and implement
rectangle rendering separately in the pixman, GLES2 and Vulkan
renderers.