The Godot API (gdnative_interface.h) allows methods to be registered on
extension classes with
`classdb_register_extension_class_method`
a `GDNativeExtensionClassMethodInfo` can be provided to this function
along with a `get_argument_info_func` which according to the comment
indicates that argument names should be definable here.
Unfortunately, setting the name field in the `GDNativePropertyInfo`
struct has no effect on the editor documentation, which continues to
display "_unnamed_arg" for each argument.
I discovered that `get_argument_info` is responsible for this as it
always overrides the `info.name`. I've added an if condition that will
only override the name when it is empty. I've tested this with my
GDExtension module and I can confirm that with this commit, the argument
name shows up in the builtin docs. eg. in Lookup Symbol.
6bc16660cc