php: Add syntax highlighting for Intelephense completions (#18774)

Release Notes:

- N/A

This PR introduces syntax highlighting for intelephense autocomple. The
styling was selected to roughly match PHPStorm's default scheme.

Please note that I'm not very familiar with writing Rust, but I'm happy
to adapt to any requested changes!

## Examples

### Object attributes, methods and constants

![Screenshot 2024-10-06 at 13 38
03](https://github.com/user-attachments/assets/a91634ff-0f2e-41f0-b548-ecb09c40947c)
![Screenshot 2024-10-06 at 13 38
11](https://github.com/user-attachments/assets/b6f179f4-898b-4d82-9d36-a3e82328325c)

### Typed enum members

![Screenshot 2024-10-06 at 13 38
53](https://github.com/user-attachments/assets/7133b981-4f68-4210-b233-403cdf3ec9bb)
![Screenshot 2024-10-06 at 13 38
41](https://github.com/user-attachments/assets/2e806f3d-3538-45f2-b075-b8be5902b786)

### Variables

Includes altered highlighting for [reserved variable
names](https://www.php.net/manual/en/reserved.variables.php).

![Screenshot 2024-10-06 at 13 39
30](https://github.com/user-attachments/assets/be426eb8-5879-432d-b302-391c2c68a7cb)

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Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>