Build/Test Tools: Improve Xdebug cross-platform compatibility.

Updates the Xdebug configuration in the local Docker environment to better support Windows (WSL2) users while maintaining stability for macOS and Linux.

* Enables `xdebug.discover_client_host` to allow Xdebug to automatically connect back to the IP address listed in the HTTP request headers, ensuring the debugger works reliably regardless of specific network topology.
* Sets `xdebug.client_host` to `host.docker.internal` as a fallback for `xdebug.discover_client_host`. In WSL2 networking, `localhost` resolves to the container itself rather than the host machine, preventing the debugger from connecting to the IDE; `host.docker.internal` correctly routes to the host machine across platforms.

Follow-up to [60060].

Reviewed-by wildworks.
Merges [61461] to the 6.9 branch.

Props SirLouen, jdeep, westonruter.
See #49953.
Fixes #63979.

git-svn-id: https://develop.svn.wordpress.org/branches/6.9@61541 602fd350-edb4-49c9-b593-d223f7449a82

Author: t-hamano

tools/local-env/php-config.ini

@@ -3,3 +3,5 @@ error_reporting = -1
 upload_max_filesize = 1G
 post_max_size = 1G
 xdebug.start_with_request=trigger
+xdebug.discover_client_host=true
+xdebug.client_host=host.docker.internal