Improvement of modal UI when modal exceeds the height of the browser

Please test this using multiple browsers and multiple screen resolutions. Test 1 (The height of the modals should not exceed the height of the browser) Login as Admin. Create a Course. Go to the Course. Click on any 'Add an activity or resource' link to activate the activity chooser. In the activity chooser, click on the "Assignment" activity. In the "Adding a new Assignment.." page, In the " Submission types " section, click on the " Choose " button (related to the " Accepted file types " field) make sure the height of the "Accepted file types" modal is less than the browser's height. inspect the code and make sure there is a class "modal-dialog-scrollable" attached to the div element with class "modal-dialog" make sure the action buttons ("Save changes", "Cancel") in the footer area are visible at all times. make sure there is a vertical scrollbar, allowing to view the rest of the content in the modal's body. Test 2 (The activity chooser modal is an exception and it's height should exceed the height of the browser in given situations) Login as Admin. Create a Course. Go to the Course. Click on any 'Add an activity or resource' link to activate the activity chooser. Once the activity chooser is displayed, click on the "All" tab and resize the browser window so it's height is less than the height of the modal. make sure the height of the "Activity chooser" modal exceeds beyond the browser's height. inspect the code and make sure there is a class "modal-dialog-scrollable"  is NOT present in the div element with class "modal-dialog" make sure a vertical scrollbar is NOT present in the modal's body.