Files API: Add Streaming file mime type support

Before applying the patch apply the following steps Set up a course in Moodle add a file resource or a resource containing a file of one (or all) of the file types listed in this issues description Click and save the the test file resource Using the browser inspector or other tool confirm that when the test file is downloaded that the mime-type sent is: For .fmp4 & .ts: "application/octet-stream" (or txt / xml, depends of the browser) For .mpd &.m3u8: their real mime-type, aka application/dash+xml and application/x-mpegURL Optionally check the 'files' table in the database that all entries with the extension of the test file added have a 'mimetype' of "application/octet-stream" After applying the patch Upgrade the site Go back to the course in Moodle with the test file Click and save the file resource Using the browser inspector or other tool confirm that when the test file is downloaded that the mime-type sent now relates to the correct type as defined in the issue description Optionally check the 'files' table in the database that all entries with the extension of the test file added have a 'mimetype'