Improve pasting (#723)

* switch to selection tool on paste

* align pasting via contextMenu with pasting from event

* ensure only plaintext can be pasted

* fix findShapeByKey regression

* simplify wysiwyg pasting

* improve wysiwyg blurriness

src/types.ts

@@ -1,4 +1,5 @@
 import { ExcalidrawElement } from "./element/types";
+import { SHAPES } from "./shapes";
 
 export type AppState = {
   draggingElement: ExcalidrawElement | null;
@@ -8,7 +9,7 @@ export type AppState = {
   // element being edited, but not necessarily added to elements array yet
   //  (e.g. text element when typing into the input)
   editingElement: ExcalidrawElement | null;
-  elementType: string;
+  elementType: typeof SHAPES[number]["value"];
   elementLocked: boolean;
   exportBackground: boolean;
   currentItemStrokeColor: string;