Update the $scheme parameter in get_rest_url()

[johnbillion]

The default value of the $scheme parameter in get_rest_url() is json. This should be changed to rest, and documentation for this value should be added to get_home_url(), home_url(), and set_url_scheme().

[rachelbaker]

get_rest_url should default to a scheme of rest

[DrewAPicture]

Whoops :)

[DrewAPicture]

In 35274:

Docs: Update the default scheme for get_rest_url() from 'json' to 'rest'.

Also adds 'rest' to the documented list of schemes for home_url(), get_home_url(), set_url_scheme(), and the home_url and set_url_scheme hooks.

Props rachelbaker.
Fixes #34300.