Support rearranging layers with hotkeys (#271)

* Support moving single layers

* Fix "Move layer to top/bottom" keybinds

* Rename things named "move" to "reorder"

Fix formatting

* Combine sorted layer helper functions

* Use integer consts for moving layers to front/back

* Fix merge mistake

* Fix some clippy lints

* Fix panic

* Remove "get" prefix from functions

* Bring layer menu items out to sub-menu

* Support moving multiple layers at a time

* Add comment explaining odd keybinding

* Add reordering tests

* Add negative test

* Add new error type

* Add layer position helper, clean up tests

* Make position helper return Result

* Clean up slice iteration

* Simplify source_layer_ids computation

Co-authored-by: Dennis Kobert <dennis@kobert.dev>

core/document/src/operation.rs

@@ -76,4 +76,8 @@ pub enum Operation {
 		path: Vec<LayerId>,
 		color: Color,
 	},
+	ReorderLayers {
+		source_paths: Vec<Vec<LayerId>>,
+		target_path: Vec<LayerId>,
+	},
 }