Extend safe name filter to support Godot 3.4 API

This PR adds 'enum' keyword to rust_safe_name filter and also makes use
of this filter for rusty_method_name variable in bindings generator. It
allows to build godot-rust with latest stable Godot 3.4 API.

Author: mivort

bindings_generator/src/lib.rs

@@ -166,6 +166,7 @@ fn rust_safe_name(name: &str) -> proc_macro2::Ident {
         "in" => format_ident!("_in"),
         "override" => format_ident!("_override"),
         "where" => format_ident!("_where"),
+        "enum" => format_ident!("_enum"),
         name => format_ident!("{}", name),
     }
 }

bindings_generator/src/methods.rs

@@ -346,7 +346,7 @@ pub(crate) fn generate_methods(
 
         icalls.insert(icall_name.clone(), method_sig);
 
-        let rusty_name = format_ident!("{}", rusty_method_name);
+        let rusty_name = rust_safe_name(rusty_method_name);
 
         let maybe_unsafe: TokenStream;
         let maybe_unsafe_reason: &str;