Rename method name to param_type.

The `node_type` is used practically only for method arguments.
Change the name to make the difference between `literal_to_type` and `node_type` clearer.

lib/rbs/prototype/rb.rb

@@ -408,7 +408,7 @@ def function_type_from_body(node, def_name)
           name = lvasgn.children[0]
           fun.optional_positionals << Types::Function::Param.new(
             name: name,
-            type: node_type(lvasgn.children[1])
+            type: param_type(lvasgn.children[1])
           )
         end
 
@@ -429,7 +429,7 @@ def function_type_from_body(node, def_name)
           when nil, :NODE_SPECIAL_REQUIRED_KEYWORD
             fun.required_keywords[name] = Types::Function::Param.new(name: name, type: untyped)
           when RubyVM::AbstractSyntaxTree::Node
-            fun.optional_keywords[name] = Types::Function::Param.new(name: name, type: node_type(value))
+            fun.optional_keywords[name] = Types::Function::Param.new(name: name, type: param_type(value))
           else
             raise "Unexpected keyword arg value: #{value}"
           end
@@ -578,7 +578,7 @@ def range_element_type(types)
         end
       end
 
-      def node_type(node, default: Types::Bases::Any.new(location: nil))
+      def param_type(node, default: Types::Bases::Any.new(location: nil))
         case node.type
         when :LIT
           case node.children[0]
@@ -610,6 +610,9 @@ def node_type(node, default: Types::Bases::Any.new(location: nil))
         end
       end
 
+      # backward compatible
+      alias node_type param_type
+
       def private
         @private ||= AST::Members::Private.new(location: nil)
       end