fix(module:code-editor): memorize cursor position and selections (#6044)

Calling #setValue() on a monaco editor instance causes the mouse cursor to jump to the
beginning of the document, which is undesirable for a ControlValueAccessor implementation
which should only update the content. Also see
microsoft/monaco-editor#1397 for more information.

Unfortunately, using #executeEdits() doesn't really work as a replacement because it will
mess with selections. Therefore we memorize and restore the cursor position before/after
setting the value. Since #setValue() also causes a selection to be lost we do the same for
those. Restoring selections may produce slightly unexpected results if the selection covers
part of the content that has been changed, but is still preferable to losing the selection
altogether.

fixes #6038

components/code-editor/code-editor.component.ts

@@ -212,7 +212,8 @@ export class NzCodeEditorComponent implements OnDestroy, AfterViewInit {
 
     if (this.nzEditorMode === 'normal') {
       if (this.modelSet) {
-        (this.editorInstance.getModel() as ITextModel).setValue(this.value);
+        const model = this.editorInstance.getModel() as ITextModel;
+        this.preservePositionAndSelections(() => model.setValue(this.value));
       } else {
         (this.editorInstance as IStandaloneCodeEditor).setModel(
           monaco.editor.createModel(this.value, (this.editorOptionCached as EditorOptions).language)
@@ -222,8 +223,10 @@ export class NzCodeEditorComponent implements OnDestroy, AfterViewInit {
     } else {
       if (this.modelSet) {
         const model = (this.editorInstance as IStandaloneDiffEditor).getModel()!;
-        model.modified.setValue(this.value);
-        model.original.setValue(this.nzOriginalText);
+        this.preservePositionAndSelections(() => {
+          model.modified.setValue(this.value);
+          model.original.setValue(this.nzOriginalText);
+        });
       } else {
         const language = (this.editorOptionCached as EditorOptions).language;
         (this.editorInstance as IStandaloneDiffEditor).setModel({
@@ -235,6 +238,30 @@ export class NzCodeEditorComponent implements OnDestroy, AfterViewInit {
     }
   }
 
+  /**
+   * {@link editor.ICodeEditor}#setValue resets the cursor position to the start of the document.
+   * This helper memorizes the cursor position and selections and restores them after the given
+   * function has been called.
+   */
+  private preservePositionAndSelections(fn: () => unknown): void {
+    if (!this.editorInstance) {
+      fn();
+      return;
+    }
+
+    const position = this.editorInstance.getPosition();
+    const selections = this.editorInstance.getSelections();
+
+    fn();
+
+    if (position) {
+      this.editorInstance.setPosition(position);
+    }
+    if (selections) {
+      this.editorInstance.setSelections(selections);
+    }
+  }
+
   private setValueEmitter(): void {
     const model = (this.nzEditorMode === 'normal'
       ? (this.editorInstance as IStandaloneCodeEditor).getModel()