Add keyboard shortcut to duplicate layers (#214)

* Add keyboard shortcut to duplicate layers

* Avoid heap allocation in DuplicateSelectedLayers

core/editor/src/input/input_mapper.rs

@@ -167,6 +167,7 @@ impl Default for Mapping {
 			entry! {action=GlobalMessage::LogInfo, key_down=Key1},
 			entry! {action=GlobalMessage::LogDebug, key_down=Key2},
 			entry! {action=GlobalMessage::LogTrace, key_down=Key3},
+			entry! {action=DocumentMessage::DuplicateSelectedLayers, key_down=KeyD, modifiers=[KeyControl]},
 		];
 		Self { up, down, pointer_move }
 	}