Make use of "VSCode" compliant with RuboCop Naming/FileName

* Rename production code and spec to `vscode_*`
* Allow acrynom `VSCode` in RuboCop configuration

.rubocop.yml

@@ -171,6 +171,7 @@ Naming/FileName:
     - ED25519
     - GitLab
     - JavaScript
+    - VSCode
     # default ones:
     - CLI
     - DSL

lib/gitlab/usage_data_counters/vs_code_extension_activity_unique_counter.rb → lib/gitlab/usage_data_counters/vscode_extension_activity_unique_counter.rb

-# rubocop:todo Naming/FileName
 # frozen_string_literal: true
 
 module Gitlab
@@ -27,5 +26,3 @@ module Gitlab
     end
   end
 end
-
-# rubocop:enable Naming/FileName