Add SPECULAR_AMOUNT spatial light shader built-in

Light3D has a light_specular property which is used to set the
intensity of specular contributed by this light source, but it was
previously only used by the default material light shader, and not
possible to use in a custom light() shader.

drivers/gles3/shaders/scene.glsl

@@ -771,7 +771,7 @@ void light_compute(vec3 N, vec3 L, vec3 V, float A, vec3 light_color, bool is_di
 	alpha = min(alpha, clamp(1.0 - attenuation, 0.0, 1.0));
 #endif
 
-#endif // LIGHT_CODE_USED
+#endif // USE_LIGHT_SHADER_CODE
 }
 
 float get_omni_spot_attenuation(float distance, float inv_range, float decay) {

drivers/gles3/storage/material_storage.cpp

@@ -1660,6 +1660,7 @@ MaterialStorage::MaterialStorage() {
 
 		//for light
 		actions.renames["VIEW"] = "view";
+		actions.renames["SPECULAR_AMOUNT"] = "specular_amount";
 		actions.renames["LIGHT_COLOR"] = "light_color";
 		actions.renames["LIGHT_IS_DIRECTIONAL"] = "is_directional";
 		actions.renames["LIGHT"] = "light";

servers/rendering/renderer_rd/forward_clustered/scene_shader_forward_clustered.cpp

@@ -641,6 +641,7 @@ void SceneShaderForwardClustered::init(const String p_defines) {
 
 		//for light
 		actions.renames["VIEW"] = "view";
+		actions.renames["SPECULAR_AMOUNT"] = "specular_amount";
 		actions.renames["LIGHT_COLOR"] = "light_color";
 		actions.renames["LIGHT_IS_DIRECTIONAL"] = "is_directional";
 		actions.renames["LIGHT"] = "light";

servers/rendering/renderer_rd/forward_mobile/scene_shader_forward_mobile.cpp

@@ -531,6 +531,7 @@ void SceneShaderForwardMobile::init(const String p_defines) {
 
 		//for light
 		actions.renames["VIEW"] = "view";
+		actions.renames["SPECULAR_AMOUNT"] = "specular_amount";
 		actions.renames["LIGHT_COLOR"] = "light_color";
 		actions.renames["LIGHT_IS_DIRECTIONAL"] = "is_directional";
 		actions.renames["LIGHT"] = "light";

servers/rendering/shader_types.cpp

@@ -187,6 +187,7 @@ ShaderTypes::ShaderTypes() {
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["UV"] = constt(ShaderLanguage::TYPE_VEC2);
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["UV2"] = constt(ShaderLanguage::TYPE_VEC2);
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["VIEW"] = constt(ShaderLanguage::TYPE_VEC3);
+	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["SPECULAR_AMOUNT"] = constt(ShaderLanguage::TYPE_FLOAT);
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["LIGHT"] = constt(ShaderLanguage::TYPE_VEC3);
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["LIGHT_COLOR"] = constt(ShaderLanguage::TYPE_VEC3);
 	shader_modes[RS::SHADER_SPATIAL].functions["light"].built_ins["LIGHT_IS_DIRECTIONAL"] = constt(ShaderLanguage::TYPE_BOOL);