Rely on requiring rubocop-ast in extension

Extensions are loaded before the host application, and we need to ensure
we patch the class before the macros are used.

lib/tapioca/dsl/extensions/rubocop.rb

@@ -1,7 +1,11 @@
 # typed: strict
 # frozen_string_literal: true
 
-return unless defined?(RuboCop::AST::NodePattern::Macros)
+begin
+  require "rubocop-ast"
+rescue LoadError
+  return
+end
 
 module Tapioca
   module Dsl