fix(drop-down): merge provided in open overlay settings

Author: wnvko

projects/igniteui-angular/src/lib/dialog/dialog.component.ts

@@ -478,6 +478,7 @@ export class IgxDialogComponent implements IToggleView, OnInit, OnDestroy, After
         const eventArgs: IDialogCancellableEventArgs = { dialog: this, event: null, cancel: false };
         this.opening.emit(eventArgs);
         if (!eventArgs.cancel) {
+            overlaySettings = { ...{}, ... this._overlayDefaultSettings, ...overlaySettings };
             this.toggleRef.open(overlaySettings);
             this.isOpenChange.emit(true);
             if (!this.leftButtonLabel && !this.rightButtonLabel) {

projects/igniteui-angular/src/lib/drop-down/drop-down.component.spec.ts

@@ -1265,7 +1265,7 @@ describe('IgxDropDown ', () => {
                 expect(dropdown.closing.emit).toHaveBeenCalledTimes(3);
                 expect(dropdown.closed.emit).toHaveBeenCalledTimes(3);
             }));
-            fit('#15137 - should bind to custom target if provided', fakeAsync(() => {
+            it('#15137 - should bind to custom target if provided', fakeAsync(() => {
                 const input = fixture.debugElement.query(By.css('input'));
                 dropdown.open({ target: input.nativeElement });
                 tick();

projects/igniteui-angular/src/lib/drop-down/drop-down.component.ts

@@ -243,7 +243,7 @@ export class IgxDropDownComponent extends IgxDropDownBaseDirective implements ID
      * ```
      */
     public open(overlaySettings?: OverlaySettings) {
-        const settings = overlaySettings || this.getDefaultOverlaySettings();
+        const settings = { ... {}, ...this.getDefaultOverlaySettings(), ...overlaySettings };
         this.toggleDirective.open(settings);
         this.updateScrollPosition();
     }