Significantly improve the speed of shader compilation in compatibility backend

Compile the unlit version by default to save on both cache size and compile time

(cherry picked from commit f1781fe9d1ec82cc9f78ecf0a8f6fa20e7114e46)

drivers/gles3/shaders/canvas.glsl

@@ -9,7 +9,7 @@ mode_instanced = #define USE_ATTRIBUTES \n#define USE_INSTANCING
 
 #[specializations]
 
-DISABLE_LIGHTING = false
+DISABLE_LIGHTING = true
 USE_RGBA_SHADOWS = false
 SINGLE_INSTANCE = false