Localize schema for wp api client

[adamsilverstein]

Fixes #1298.

• Localize the WP-API schema so the client can initialize immediately, without making an ajax request.
• Remove the wait for wp.api.init - the client is now ready immediately after loading and this is no longer required
• Add a filter to the wp-api settings so developers can adjust the default settings used,

[nylen]

Nice enhancement for the short- to medium-term, avoids an API request on load.

Longer-term, I wonder if we can do a better job of providing this functionality in core. The wp_deregister_script / wp_register_script dance seems like a bit of a hack.

[nylen]

You can use rest_do_request instead of $wp_rest_server->dispatch, as done elsewhere in the codebase.

[nylen]

This should probably be a Gutenberg-specific filter name, no?

[westonruter]

This reminds me of WP-API/client-js#68

[westonruter]

Should this block not be replaced with $wp_rest_server = rest_get_server(), and then eliminate the global?

[nylen]

Even better: rest_do_request as noted above

[nylen]

In general I am not very fond of the fact that this operation (fetching the entire schema) is necessary at all. Whether it's done on the client side through an API call, or pre-initialized on the server side, this is a very expensive operation.

[aduth]

Superseded by #2057