Issue #5174 Make timepicker output format configurable

[ndewhurst]

Proposed changes

Allow timepickers to be configured with a "format" option similar to
that used by datepickers. E.g. { format: "HH:mm" }
or { format: "hh:mm A" }. Accommodate 12-hour and 24-hour modes, and
allow users to specify output formats using any of the following
elements:

• 24-hour format of the hour, with or without leading zeros
• 12-hour format of the hour, with or without leading zeros
• Minutes, with or without leading zeros
• Seconds, with or without leading zeros (currently defaults to 0/00)
• Uppercase or lowercase ante/post meridian (AM/PM)

This will allow the use of timepickers with HTML inputs of type "time"
in browsers that perform validation and reject the default format for
12-hour mode ("hh:mm A" - e.g. "12:45 AM").

See issue #5174.

Screenshots (if appropriate) or codepen:

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.