gdextension: `Object::ConnectFlags` marked as not a bitfield in `extension_api.json`

### Tested versions

- Reproducible in: 4.3.stable.official.77dcf97d8

### System information

Godot v4.3.stable - Ubuntu 24.04.1 LTS 24.04 - Wayland - Vulkan (Forward+) - dedicated AMD Radeon RX Vega M GH Graphics (RADV VEGAM) - Intel(R) Core(TM) i7-8809G CPU @ 3.10GHz (8 Threads)

### Issue description

In `extension_api.json`, `Object::ConnectFlags` is marked as `"is_bitfield": false`, however, given that the enum values are powers of two, the default value in e.g. `Signal::connect` is 0 (seemingly unset), and that the behaviors associated with each enum variant are seemingly orthogonal, it would seem that this is a bitfield.

This seems to have led to issues in C# (https://github.com/godotengine/godot/issues/74829) and in Rust gdext (https://github.com/godot-rust/gdext/issues/756).

### Steps to reproduce

```sh
godot --dump-extension-api
cat extension_api.json | jq '.classes[] | select(.name == "Object").enums[] | select(.name == "ConnectFlags").is_bitfield'
# false
# alternately, inspect with a pager or text editor
```

### Minimal reproduction project (MRP)

N/A

Start by running `godot --dump-extension-api` and inspecting `extension_api.json` for `Object::ConnectFlags`, then trace how its bitfield status is determined. Compare the enum values and generated metadata with the reported C# and Rust gdext issues; done means the generated API reports the correct status and the relevant regression is covered.

Written by the indexing model from the issue text.