[edition] Add a FreeText editor (#14970)

- add a basic UI to edit some text in a pdf;
- an editor can be moved, suppressed, cut, copied, pasted, selected;
- add an undo/redo manager.

test/integration-boot.js

@@ -30,6 +30,7 @@ async function runTests(results) {
       "annotation_spec.js",
       "accessibility_spec.js",
       "find_spec.js",
+      "freetext_editor_spec.js",
     ],
   });