REST API: remove unneeded pre-theme-loading functionality, was used to work around Twenty Eleven being the active theme.

See #3046..

Merges r104816-wpcom.
REST API

When loading the theme context (functions.php - so we get CPTS, etc), also load the Jetpack compat files.
Adds tests to test the functionality of getting iS settings (usually stored in the jetpack.php file).

Merges r104920-wpcom.
REST API

Load the new post formats endpoints and provide some tests to make sure they work as expected.
see [104371] and [104372]
https://github.com/Automattic/beep-beep-boop/issues/48

Merges r104373-wpcom.
REST API

Mark the post formats endpoint as undocumented for now

Merges r104390-wpcom.
REST API: Add support for "auto-draft" post status

This adds support for auto-drafts, which are temporary
placeholders created under the hood when the new post
page is loaded up, reserving a post ID so that e.g.
embed/shortcode previewing works.

Merges r104664-wpcom.
REST API: when parsing the args in the taxonomy endpoint, remove the `fields` arg as it's used for output filtering on the final output and not as part of the args used to fetch the categories themselves

Merges r104968-wpcom.