Collision on `CONNECT_DEFERRED`

### Godot version

4.5

### godot-cpp version

4.5

### System information

Windows 11

### Issue description

The Windows SDK defines `CONNECT_DEFERRED` as a hex value with a preprocessor statement in `winnetwk.h`. However, Godot’s `Object` class uses it as an enum value name inside `ConnectFlags`.

A fix is present inside `godot_cpp/core/defs.hpp`:
`#undef CONNECT_DEFERRED // override from Windows SDK, clashes with Object enum`

The issue is that the header is `#pragma once`, meaning that if `defs.hpp` is ever included before the Windows SDK, the fix stops working because the header can't be included again. In a large codebase, making sure that the right include order is respected everywhere is a very complex task.

A way to make this fix more reliable would be to move the `#undef` statements inside `defs.hpp` to another header that doesn't have a `#pragma once` directive. They are already guarded by `#ifdef` clauses, so this should be okay in theory.

### Steps to reproduce

- Include any Godot header that has `godot_cpp/core/defs.hpp` in its include chain
- Include `Windows.h`
- Include `godot_cpp/core/defs.hpp`
- Try to use `CONNECT_DEFERRED`: Windows's define hasn't been undefined by `defs.hpp`

### Minimal reproduction project

Compile with `scons`, the following errors are thrown:
- 'constant': illegal token on right side of '::'
- type 'unknown-type' unexpected

See `src\example_class.h` for the problematic code and explanation comments.

[GDExample.zip](https://github.com/user-attachments/files/25492175/GDExample.zip)