Add LIGHT_VERTEX to fragment shader

Adds a new variable to the fragment shader to specify
the vertex position used when calculating lighting.

servers/rendering/renderer_rd/shaders/forward_mobile/scene_forward_mobile.glsl

@@ -830,6 +830,10 @@ void main() {
 	inv_view_matrix[2][3] = 0.0;
 #endif
 
+#ifdef LIGHT_VERTEX_USED
+	vec3 light_vertex = vertex;
+#endif //LIGHT_VERTEX_USED
+
 	mat4 read_view_matrix = scene_data.view_matrix;
 	vec2 read_viewport_size = scene_data.viewport_size;
 
@@ -837,6 +841,15 @@ void main() {
 #CODE : FRAGMENT
 	}
 
+#ifdef LIGHT_VERTEX_USED
+	vertex = light_vertex;
+#ifdef USE_MULTIVIEW
+	view = -normalize(vertex - eye_offset);
+#else
+	view = -normalize(vertex);
+#endif //USE_MULTIVIEW
+#endif //LIGHT_VERTEX_USED
+
 #ifdef LIGHT_TRANSMITTANCE_USED
 #ifdef SSS_MODE_SKIN
 	transmittance_color.a = sss_strength;