[6.x] Time field enhancements

[jasonvarga]

This PR adds:

• An augment_format option to the time fieldtype.
  This will allow you to use {{ time_field }} by itself on the frontend and it will output the appropriate format with needing any modifiers.

• A format_time modifier
  This can be chained into a time and will convert it to the given format.
  It bypasses any of the timezone logic that the other date modifiers use.
  e.g. {{ "13:45" | format_time('g:ia') }} outputs 1:45pm
  It will use g:ia by default so you don't even need to pass the format.
  e.g. {{ "13:45" | format_time }} outputs 1:45 too.

Closes #13766

[jackmcdade]

Works great!