Some script editor text colors are not changeable

### Tested versions

4.7 dev 1

### System information

Windows

### Issue description

After customizing my script editor theme, I found out that some GDScript text is not highlighted by any of the customizable colors in `"text_editor/theme/highlighting"`, but are colored in gray:

- enum constant names in the enum definition

- parameters and local variables in functions

### Steps to reproduce

N/A, visible even in the default theme.

### Minimal reproduction project (MRP)

It's about editor settings.