php: Highlight PHPDoc comments (#11695)

This adds highlighting of phpdoc tags and PHP types to phpdoc comments,
using
[tree-sitter-phpdoc](https://github.com/claytonrcarter/tree-sitter-phpdoc)
(maintained by yours me, and also in use by neovim).

<table>
<tr>
<td>
<strong>Before</strong>
<img
src="https://github.com/zed-industries/zed/assets/1420419/bae4c502-8a2c-4399-893f-fcff4e5797b6">
</td>
<td>
<strong>After</strong>
<img
src="https://github.com/zed-industries/zed/assets/1420419/8848e9fb-61a0-4938-a118-7041da9589c0">
</td>
</tr>
</table>


Release Notes:

- N/A

extensions/php/extension.toml

@@ -15,3 +15,7 @@ language_ids = { PHP = "php"}
 repository = "https://github.com/tree-sitter/tree-sitter-php"
 commit = "8ab93274065cbaf529ea15c24360cfa3348ec9e4"
 path = "php"
+
+[grammars.phpdoc]
+repository = "https://github.com/claytonrcarter/tree-sitter-phpdoc"
+commit = "1d0e255b37477d0ca46f1c9e9268c8fa76c0b3fc"