DEV: Switch to pnpm for JS dependencies (#28671)

This will bring significant improvements to install speed & storage requirements. For information on how it may affect you, see https://meta.discourse.org/t/324521

This commit:
- removes the `yarn.lock` and replaces with `pnpm-lock.yaml`
- updates workspaces to pnpm format
- adjusts package dependencies to work with pnpm's stricter resolution strategy
- updates Rails app to load modules from more specific node_modules directories
- adds a `.pnpmfile` which automatically cleans up old yarn-managed `node_modules` directories
- updates various scripts to call `pnpm` instead of `yarn`
- updates patches to use pnpm's native patch system instead of patch-package
- adds a patch for licensee to support pnpm

lib/highlight_js.rb

@@ -1,7 +1,8 @@
 # frozen_string_literal: true
 
 module HighlightJs
-  HIGHLIGHTJS_DIR ||= "#{Rails.root}/node_modules/@highlightjs/cdn-assets/"
+  HIGHLIGHTJS_DIR ||=
+    "#{Rails.root}/app/assets/javascripts/discourse/node_modules/@highlightjs/cdn-assets/"
   VERSION ||= 1 # bump to invalidate caches following core changes
 
   def self.languages