Add a new renderer API

Goals:

- Extensibility: we need to be able to add new params to the calls
  to render a texture/rect. For instance we'll need to add fences to
  the render texture operation for explicit sync purposes.
- No implicit state: no more bind_buffer, begin, end.
- No matrices: these hurt Pixman and we don't need them.
- Clip regions for optimized damage repainting.

Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3188

render/pass.c

@@ -0,0 +1,25 @@
+#include <assert.h>
+#include <string.h>
+#include <wlr/render/interface.h>
+#include <wlr/render/wlr_renderer.h>
+
+void wlr_render_pass_init(struct wlr_render_pass *render_pass,
+		const struct wlr_render_pass_impl *impl) {
+	assert(impl->submit && impl->add_texture && impl->add_rect);
+	memset(render_pass, 0, sizeof(*render_pass));
+	render_pass->impl = impl;
+}
+
+bool wlr_render_pass_submit(struct wlr_render_pass *render_pass) {
+	return render_pass->impl->submit(render_pass);
+}
+
+void wlr_render_pass_add_texture(struct wlr_render_pass *render_pass,
+		const struct wlr_render_texture_options *options) {
+	render_pass->impl->add_texture(render_pass, options);
+}
+
+void wlr_render_pass_add_rect(struct wlr_render_pass *render_pass,
+		const struct wlr_render_rect_options *options) {
+	render_pass->impl->add_rect(render_pass, options);
+}