docs: add a callout that adding/removing to formArray doesn't not mark dirty (angular#64337)

fixes angular#36788

PR Close angular#64337

Author: JeanMeche

packages/forms/src/model/form_array.ts

@@ -174,6 +174,8 @@ export class FormArray<TControl extends AbstractControl<any> = any> extends Abst
    * * `emitEvent`: When true or not supplied (the default), both the `statusChanges` and
    * `valueChanges` observables emit events with the latest status and value when the control is
    * inserted. When false, no events are emitted.
+   *
+   * NOTE: Pushing to the FormArray will not mark it dirty. If you want to mark if dirty, call `markAsDirty()`.
    */
   push(control: TControl | Array<TControl>, options: {emitEvent?: boolean} = {}): void {
     if (Array.isArray(control)) {
@@ -201,6 +203,8 @@ export class FormArray<TControl extends AbstractControl<any> = any> extends Abst
    * * `emitEvent`: When true or not supplied (the default), both the `statusChanges` and
    * `valueChanges` observables emit events with the latest status and value when the control is
    * inserted. When false, no events are emitted.
+   *
+   * NOTE: Inserting to the FormArray will not mark it dirty. If you want to mark if dirty, call `markAsDirty()`.
    */
   insert(index: number, control: TControl, options: {emitEvent?: boolean} = {}): void {
     this.controls.splice(index, 0, control);
@@ -220,6 +224,8 @@ export class FormArray<TControl extends AbstractControl<any> = any> extends Abst
    * * `emitEvent`: When true or not supplied (the default), both the `statusChanges` and
    * `valueChanges` observables emit events with the latest status and value when the control is
    * removed. When false, no events are emitted.
+   *
+   * NOTE: Removing the FormArray will not mark it dirty. If you want to mark if dirty, call `markAsDirty()`.
    */
   removeAt(index: number, options: {emitEvent?: boolean} = {}): void {
     // Adjust the index, then clamp it at no less than 0 to prevent undesired underflows.