Making this validation code public allows projects to validate a GParamSpec name before creating it. While hard-coded GParam don't need this, we can't afford crashing the main program for dynamically generated GParam from user-created data.
In such case, we will need to validate the param names and return errors instead of trying to create a GParam with these names.
Some context: in GIMP, we have various usages of dynamically generated GParamSpec, for instance for API created by plug-ins. Therefore this is user-provided data, which can be invalid for GParamSpec arguments. Right now, we don't validate the data, which means a user-provided plug-in has the ability to crash GIMP core by providing an invalid name. That's not cool.
Obviously we could just reimplement/copy-paste the validation code, but since it obviously already exist in glib, it seems a bit stupid. Moreover if the code/rules ever change on glib side and we don't notice it, we might end up with inconsistent check. So I'm just suggesting for this existing function to become public.