Curves: make the "surface_uv_map" a searchable dropdown

The users had to type in a name here, but we can also make it a dropdown
choice with existing UV Maps for convenience:
- dont have to remember a name or copy paste obviously
- shows in red if it was removed / invalid

Came up in T101028

Maniphest Tasks: T101028

Differential Revision: https://developer.blender.org/D15956

release/scripts/startup/bl_ui/properties_data_curves.py

@@ -44,7 +44,13 @@ class DATA_PT_curves_surface(DataButtonsPanel, Panel):
         layout.use_property_split = True
 
         layout.prop(ob.data, "surface")
-        layout.prop(ob.data, "surface_uv_map", text="UV Map")
+        has_surface = ob.data.surface is not None
+        if has_surface:
+            layout.prop_search(ob.data, "surface_uv_map", ob.data.surface.data, "uv_layers", text="UV Map")
+        else:
+            row = layout.row()
+            row.prop(ob.data, "surface_uv_map", text="UV Map")
+            row.enabled = has_surface
 
 
 class CURVES_MT_add_attribute(Menu):