New function: human_readable_duration

In WordPress 5.1, the new human_readable_duration function will be introduced. This function accepts a duration in hours, minutes and seconds and returns a “human readable” string appropriate for screen readers.

The function takes a string representing a time duration, with hours, minutes and seconds separated by a : (colon). For example, calling human_readable_duration( '3:10' ); will return 3 minutes, 10 seconds. Minutes and seconds are required. For 10 seconds, the call would be human_readable_duration( '0:10' );.

This new function was added as part of the work to improve the display of media metadata in #39667 where, in addition to adding units, aria-labels with plain language descriptions were added to improve accessibility:
Improved time duration accessibility in the media library using the human_readable_duration() function.

#5-1, #dev-notes