Implement frame node for MDL via scene data (#2823)

As discussed in Slack.

Author: pablode

source/MaterialXGenMdl/mdl/materialx/stdlib_1_8.mdl

@@ -83,7 +83,6 @@ export using .::stdlib_1_7 import mx_texcoord_vector3;
 export using .::stdlib_1_7 import mx_geomcolor_float;
 export using .::stdlib_1_7 import mx_geomcolor_color3;
 export using .::stdlib_1_7 import mx_geomcolor_color4;
-export using .::stdlib_1_7 import mx_frame_float;
 export using .::stdlib_1_7 import mx_time_float;
 export using .::stdlib_1_7 import mx_modulo_color3;
 export using .::stdlib_1_7 import mx_modulo_color4;
@@ -447,3 +446,11 @@ export float3 mx_viewdirection_vector3(
 			::state::coordinate_object,
 			internal_space_direction));
 }
+
+export float mx_frame_float()
+	[[
+		anno::description("Node Group: application")
+	]]
+{
+	return scene::data_lookup_float("FRAME", 1.0);
+}

source/MaterialXGenMdl/mdl/materialx/stdlib_1_9.mdl

@@ -84,7 +84,6 @@ export using .::stdlib_1_7 import mx_texcoord_vector3;
 export using .::stdlib_1_7 import mx_geomcolor_float;
 export using .::stdlib_1_7 import mx_geomcolor_color3;
 export using .::stdlib_1_7 import mx_geomcolor_color4;
-export using .::stdlib_1_7 import mx_frame_float;
 export using .::stdlib_1_7 import mx_time_float;
 export using .::stdlib_1_7 import mx_modulo_color3;
 export using .::stdlib_1_7 import mx_modulo_color4;
@@ -339,6 +338,7 @@ export using .::stdlib_1_8 import mx_geompropvalue_vector2;
 export using .::stdlib_1_8 import mx_geompropvalue_vector3;
 export using .::stdlib_1_8 import mx_geompropvalue_vector4;
 export using .::stdlib_1_8 import mx_viewdirection_vector3;
+export using .::stdlib_1_8 import mx_frame_float;