CodeMirror: +rectangularSelection and crosshairCursor as def extensions

These were default in CM5

To be added to the preferences panel once that's a thing (T359498)

Change-Id: I5a8b330444dd2dff0acfbd8e2d429a5b5273cd61

src/codemirror.js

@@ -1,5 +1,13 @@
 import { EditorState, Extension } from '@codemirror/state';
-import { EditorView, ViewUpdate, drawSelection, lineNumbers, highlightSpecialChars, keymap } from '@codemirror/view';
+import {
+	EditorView,
+	drawSelection,
+	lineNumbers,
+	highlightSpecialChars,
+	keymap,
+	rectangularSelection,
+	crosshairCursor
+} from '@codemirror/view';
 import { defaultKeymap, history, historyKeymap } from '@codemirror/commands';
 import { searchKeymap } from '@codemirror/search';
 import { bracketMatching } from '@codemirror/language';
@@ -94,7 +102,9 @@ class CodeMirror {
 				...searchKeymap
 			] ),
 			EditorState.allowMultipleSelections.of( true ),
-			drawSelection()
+			drawSelection(),
+			rectangularSelection(),
+			crosshairCursor()
 		];
 
 		// Add extensions relevant to editing (not read-only).