Add extra context to the `xmlrpc_call` action

[dd32]

The xmlrpc_call action currently passes the method name to the action, but fails to pass the arguments presented. That can make the action hard to use when the call passes specific content in the payload of the request.

For example, when the wp.getRevisions XML-RPC call is made, it's impossible to tell what post is being accessed via the API for dynamic filtering without reaching into the internals of the global $wp_xmlrpc_server object.

The attached PR simply adds the $args parameter to the action call along with the RPC server for consistency sake.

Trac ticket: https://core.trac.wordpress.org/ticket/52524

[SergeyBiryukov]

In 50353:

XML-RPC: Pass the method arguments and the XML-RPC server instance to the xmlrpc_call action.

This provides better context and makes the action easier to use when the call passes specific content in the payload of the request.

Props dd32.
Fixes #52524.

https://core.trac.wordpress.org/changeset/50353

Trac ticket: https://core.trac.wordpress.org/ticket/52524

[dd32]

Re-opening for PR 1073 above, my PR incorrectly used $args for two methods which have no args. This patch simply replaces it with an empty array.

Fixes the following PHP Notices:

E_NOTICE: Undefined variable: args in wp-includes/class-wp-xmlrpc-server.php:6652
E_NOTICE: Undefined variable: args in wp-includes/class-wp-xmlrpc-server.php:6664

[SergeyBiryukov]

In 50499:

XML-RPC: Pass an empty array to the xmlrpc_call action in methods that have no arguments.

This avoids an "Undefined variable" PHP notice in the ::mt_supportedMethods() and ::mt_supportedTextFilters() methods.

Follow-up to [50353].

Props dd32.
Fixes #52524.

[SergeyBiryukov]

In 50500:

XML-RPC: Pass an empty array to the xmlrpc_call action in methods that have no arguments.

This avoids an "Undefined variable" PHP notice in the ::mt_supportedMethods() and ::mt_supportedTextFilters() methods.

Follow-up to [50353].

Props dd32.
Reviewed by dd32, SergeyBiryukov.
Merges [50499] to the 5.7 branch.
Fixes #52524.

Thanks for the PR! Merged in r50499.