debugger: Remove PHP debug adapter (#34020)

This commit removes the PHP debug adapter in favor of a new version
(0.3.0) of PHP extension.
The name of a debug adapter has been changed from "PHP" to "Xdebug",
which makes this a breaking change in user-configured scenarios

Release Notes:

- debugger: PHP debug adapter is no longer shipped in core Zed editor;
it is now available in PHP extension (starting with version 0.3.0). The
adapter has been renamed from `PHP` to `Xdebug`, which might break your
user-defined debug scenarios.

crates/task/src/vscode_debug_format.rs

@@ -90,7 +90,7 @@ fn task_type_to_adapter_name(task_type: &str) -> String {
         "pwa-node" | "node" | "node-terminal" | "chrome" | "pwa-chrome" | "edge" | "pwa-edge"
         | "msedge" | "pwa-msedge" => "JavaScript",
         "go" => "Delve",
-        "php" => "PHP",
+        "php" => "Xdebug",
         "cppdbg" | "lldb" => "CodeLLDB",
         "debugpy" => "Debugpy",
         "rdbg" => "rdbg",