Add a search bar to allow filtering on files and Canvas pages picker

Our file picker (and the upcoming Canvas Pages picker) display an non-paginated list of documents with everything in the active folder or course.

The contents can potentially grow, specially in Canvas, which does not support folders and returns all files in a flat list, making it harder for users to find the right document.

It has been suggested that having a search input that filters the list would be very useful here.