Make playgrounds become proper JavaScript environments.

• Update syntaxes.
  • Replace the MongoDB-TmLanguage grammar with the MongoDB injection grammar.
  • Modify the `update-grammar` script to update the MongoDB injection grammar with the most recent DevTools constants during the build process.
• Activate the extension on `javascript` and `plaintext` languages.
  • Refactor activation events.
  • For playgrounds opened from the disc set JavaScript language to the document.
• Identify playgrounds based on the document path.
  • Implement the `isPlayground` util function that will identify playgrounds among other JavaScrip files.
  • Refactor all places that check for `mongodb` language id and replace it with `isPlayground` check.
• Create playgrounds as JavaScript documents.
  • Create playgrounds by the document UID.
  • Apply required changes to all templates based on playgrounds functionality (clone document, insert document, create collection, create index, search).
• Declare global variables in playground templates to resolve linting errors.
• Show the “Run Playground” button only for MongoDB playgrounds and hide it for regular JavaScript files in a workspace.
• Show Active Connection CodeLens only for MongoDB playgrounds and hide it for regular JavaScript files in a workspace.
• Show Playground Selected CodeAction only for MongoDB playgrounds and hide it for regular JavaScript files in a workspace.
• Update the Language Server to work with JavaScript documents.