Supprot RuboCop's LSP mode (#1453)

Resolves #1449.

This PR applies `RuboCop::LSP.enable`, which is the minimal API for RuboCop to handle in the context of LSP:
https://docs.rubocop.org/rubocop/1.61/usage/lsp.html#language-server-development

Furthermore, `RuboCop::LSP.enable` method and `RuboCop::LSP` module were introduced in RuboCop 1.61.0.
This PR ensures compatibility with existing versions of RuboCop dependencies.
However, in older versions of RuboCop prior to 1.60, `AutoCorrect: contextual` behaves the same as `AutoCorrect: true`.

Author: koic

lib/ruby_lsp/requests/support/rubocop_runner.rb

@@ -13,6 +13,10 @@
   raise StandardError, "Incompatible RuboCop version. Ruby LSP requires >= 1.4.0"
 end
 
+if RuboCop.const_defined?(:LSP) # This condition will be removed when requiring RuboCop >= 1.61.
+  RuboCop::LSP.enable
+end
+
 module RubyLsp
   module Requests
     module Support