fix(modal): add typing for modalRef.componentInstance (#2815)

Fixes #2479

src/modal/modal-ref.ts

@@ -30,7 +30,7 @@ export class NgbActiveModal {
 /**
  * A reference to the newly opened modal returned by the `NgbModal.open()` method.
  */
-export class NgbModalRef {
+export class NgbModalRef<T = any> {
   private _resolve: (result?: any) => void;
   private _reject: (reason?: any) => void;
 
@@ -39,7 +39,7 @@ export class NgbModalRef {
    *
    * When a `TemplateRef` is used as the content or when the modal is closed, will return `undefined`.
    */
-  get componentInstance(): any {
+  get componentInstance(): T extends new (...args: any[]) => any? InstanceType<T>: undefined {
     if (this._contentRef && this._contentRef.componentRef) {
       return this._contentRef.componentRef.instance;
     }

src/modal/modal.spec.ts

@@ -1087,7 +1087,7 @@ export class WithSkipTabindexFirstFocusableModalCmpt {
 })
 class TestComponent {
   name = 'World';
-  openedModal: NgbModalRef;
+  openedModal: NgbModalRef<string>;
   show = true;
   @ViewChild('content', {static: true}) tplContent;
   @ViewChild('destroyableContent', {static: true}) tplDestroyableContent;

src/modal/modal.ts

@@ -25,7 +25,7 @@ export class NgbModal {
    *
    * Also see the [`NgbModalOptions`](#/components/modal/api#NgbModalOptions) for the list of supported options.
    */
-  open(content: any, options: NgbModalOptions = {}): NgbModalRef {
+  open<T>(content: T, options: NgbModalOptions = {}): NgbModalRef<T> {
     const combinedOptions = Object.assign({}, this._config, options);
     return this._modalStack.open(this._moduleCFR, this._injector, content, combinedOptions);
   }