Extract PHP support into an extension (#9966)

This PR extracts PHP support into an extension and removes the built-in
PHP support from Zed.

There's a small workaround necessary in order for us to provide the
`language_ids` on the `LspAdapter` that are needed for the language
server to run properly. Eventually we'll want to build this into the
extension API, but for now we're just hard-coding it on the host side.

Release Notes:

- Removed built-in support for PHP, in favor of making it available as
an extension. The PHP extension will be suggested for download when you
open a `.php` file.

crates/extensions_ui/src/extension_suggest.rs

@@ -36,6 +36,7 @@ fn suggested_extensions() -> &'static HashMap<&'static str, Arc<str>> {
             ("latex", "tex"),
             ("make", "Makefile"),
             ("nix", "nix"),
+            ("php", "php"),
             ("prisma", "prisma"),
             ("purescript", "purs"),
             ("r", "r"),