feat(mat-datepicker): Use mat-datepicker-actions without losing the regular behavior

### Feature Description

As soon as any actions are set (in my case just a _Today_ button) the default functionality is los. Imho this should only be the case, if the `matDatepickerApply` directive is used, too.

### Use Case

Add a _Today_ button, keeping the default select behavior.

Start at the mat-datepicker-actions entry point and reproduce the reported case with a Today button. Compare behavior with and without the matDatepickerApply directive; done means the regular select behavior remains unless that directive is used.

Written by the indexing model from the issue text.