What are the keywords referenced by ios platform in *.gdextension？

### Godot version

4.0.4

### godot-cpp version

4.0

### System information

iPhone X

### Issue description

What are the keywords referenced by ios platform in *.gdextension？
What is the key for ios? Whether I defined it correctly, there is no mention of ios in the use case
```
macos.debug = "res://gdnative/osx/FMGDNative_Mac.framework"
macos.release = "res://gdnative/osx/FMGDNative_Mac.framework"
android.debug.x86_64 = ""
android.release.x86_64 = ""
android.debug.arm64 = ""
android.release.arm64 = ""
ios.debug.x86_64 = "res://gdnative/ios/FMGDNative_iOS.framework"
ios.release.x86_64 = "res://gdnative/ios/FMGDNative_iOS.framework"
ios.debug.arm64 = "res://gdnative/ios/FMGDNative_iOS.framework"
ios.release.arm64 = "res://gdnative/ios/FMGDNative_iOS.framework"
```

### Steps to reproduce

check https://github.com/godotengine/godot-cpp/blob/master/test/project/example.gdextension

### Minimal reproduction project

none