Introduce rest_get_request_from_url() for getting a WP_REST_Request object from a provided URL

[danielbachhuber]

rest_get_request_from_url() makes it easier to get a WP_REST_Request object from a provided URL. Because _links are the full URL, and not just the route, we should have a mechanism for resolving these URLs to WP_REST_Request objects.

As a matter of fact, I'm pretty sure WP_REST_Server::embed_links() doesn't work right now when pretty permalinks are disabled.

Originally ​https://github.com/WP-API/WP-API/issues/2109

[danielbachhuber]

@joehoyle @rmccue @rachelbaker Feedback on this when you have a moment. Couple of pieces I didn't get to in this first patch:

1. When the $url is to a different domain, we should return false instead of creating a WP_REST_Request object.
2. Needs to be hooked into WP_REST_Server::embed_links() and make sure we have sufficient test coverage.

[danielbachhuber]

Oops, I already found the non-pretty permalinks bug :) #35629

[chriscct7]

Crossposting from slack:

@danielbachhuber: @joehoyle @rachelbaker @rmccue could I get feedback on https://core.trac.wordpress.org/ticket/35803 pretty please?

[rmccue]

Sorry for the delayed response! LGTM; not the nicest code, but not much you can do about that. I'm not sure on the naming though; what about WP_REST_Request::from_url() ?

[rmccue]

Move to WP_REST_Request::from_url and rework internals

[rmccue]

Combine filters

[rmccue]

Simplify parse_url call

[rmccue]

In 36673:

REST API: Add WP_REST_Request::from_url()

Allows converting a REST URL into a Request object.

Props danielbachhuber.
Fixes #35803.

[rmccue]

In 36674:

REST API: Use WP_REST_Request::from_url() when embedding.

See #35803.

[DrewAPicture]

In 37013:

Docs: Improve the DocBlock for WP_REST_Request::from_url(), introduced in [36673].

See #35803. See #35986.

[DrewAPicture]

In 37014:

Docs: Improve parameter description syntax in the hook doc for the rest_request_from_url filter, introduced in [36673].

See #35803. See #35986,

[rachelbaker]

In 37021:

REST API: Remove unused variable $api_root from WP_Rest_Server->embed_links() method.

After [r36674] the variable $api_root is no longer used in this method and should be removed.

See #35803.