Add hx4compat library support

## Feature Request

It would be very useful if the **hx4compat** library could be added as an available dependency in [try.haxe.org](https://try.haxe.org).

### Motivation
- `hx4compat` provides compatibility helpers for Haxe 4, making it easier to run and test projects that depend on it.
- Adding this library would allow developers to experiment with legacy code and ensure smooth migration when using the playground.

### Benefits
- Broader compatibility for code snippets shared on try.haxe.org.
- Makes the playground more representative of real-world projects that rely on `hx4compat`.
- Improves developer experience for those testing Haxe 4 → Haxe 5 migration paths.

### Suggested Solution
Include `hx4compat` in the list of libraries available to import within try.haxe.org.

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Thanks in advance for considering this request!