Use specialization constants in clustered renderer

* Keep track of when projector, softshadow or directional sofshadow were enabled.
* Enable them via specializaton constant where it makes sense.
* Re-implements soft shadows.
* Re-implements light projectors.

servers/rendering/renderer_rd/shaders/scene_forward_mobile.glsl

@@ -370,6 +370,13 @@ void main() {
 
 #VERSION_DEFINES
 
+/* Specialization Constants */
+
+//unused but there for compatibility
+layout(constant_id = 0) const bool sc_use_forward_gi = false;
+layout(constant_id = 1) const bool sc_use_light_projector = false;
+layout(constant_id = 2) const bool sc_use_light_soft_shadows = false;
+
 /* Include our forward mobile UBOs definitions etc. */
 #include "scene_forward_mobile_inc.glsl"