Wire up module loading to application startup (#21703)

* Early module loader bundler

* Add a module installer script

* Add dev-friendly docs

* Add real module-api dependency

* Speed up `yarn add` for mulitple modules

* Fix version check for modules

* Appease the linter

.eslintrc.js

@@ -18,7 +18,7 @@ module.exports = {
         }
     },
     overrides: [{
-        files: ["src/**/*.{ts,tsx}"],
+        files: ["src/**/*.{ts,tsx}", "module_system/**/*.{ts,tsx}"],
         extends: [
             "plugin:matrix-org/typescript",
             "plugin:matrix-org/react",