Responsive image formatter for media image field

Problem/Motivation

Responsive image formatter is not available for Media Field.

Steps to reproduce

1. Create an image media field on a content type.
2. Create a "Responsive Image style" with different image-styles according breakpoint.
3. Try to add the "Responsive Image Style" in "Image formatter" on the Manage Display tab.
4. Cannot choose "Responsive Image style".

Proposed resolution

Add a responsive image formatter to the Media module which allows responsive image styles to be added to media fields.

Remaining tasks

• Address feedback in #13
• Update Issue Summary per #15

User interface changes

Manage display for an image media field on a content type:

API changes

None

Data model changes

Adds a field.formatter.settings.media_responsive_thumbnail schema.

Release notes snippet

Media fields can now be formatted as responsive image styles using a new responsive image formatter.