DEV: Remove vendored babel and update config for plugins/themes (#17832)

The new plugin list is based on the ones currently used in our ember-cli pipeline, and are based on our official browser support policy.

This commit includes an update to the raw-handlebars compiler to remove the 'very hacky but lets us use ES6' code. It's  served us well for the last 6 years, but the babel config changes broke it (`const` -> `let`). This commit takes the opportunity to refactor it to take a similar approach to PrettyText, by leaning on `mini-loader.js`.

app/assets/javascripts/discourse/package.json

@@ -17,6 +17,7 @@
   },
   "dependencies": {
     "@babel/core": "^7.18.5",
+    "@babel/standalone": "^7.18.12",
     "@discourse/itsatrap": "^2.0.10",
     "@ember/jquery": "^2.0.0",
     "@ember/optional-features": "^2.0.0",

app/assets/javascripts/yarn.lock

@@ -957,6 +957,11 @@
   dependencies:
     regenerator-runtime "^0.13.4"
 
+"@babel/standalone@^7.18.12":
+  version "7.18.12"
+  resolved "https://registry.yarnpkg.com/@babel/standalone/-/standalone-7.18.12.tgz#4c0abdf1b5213394e73a0ba5500dcc287194a20d"
+  integrity sha512-wDh3K5IUJiSMAY0MLYBFoCaj2RCZwvDz5BHn2uHat9KOsGWEVDFgFQFIOO+81Js2phFKNppLC45iOCsZVfJniw==
+
 "@babel/template@^7.16.7", "@babel/template@^7.18.6":
   version "7.18.6"
   resolved "https://registry.yarnpkg.com/@babel/template/-/template-7.18.6.tgz#1283f4993e00b929d6e2d3c72fdc9168a2977a31"