Migrate a vue.js 2 application to the vue-compat build of vue 3.0

[dwgray]

The master branch represents a vue 2.0 project create via the vue cli with typescript enabled.
The vue-compat branch is the minimal set of changes described in the migration build guide to get the application to build.
While this builds clean and appears to be using the migration build - e.g. I get a warning like this:

vue.runtime.esm-bundler.js?fe26:1595 
        
       [Vue warn]: (deprecation GLOBAL_EXTEND) Vue.extend() has been removed in Vue 3. Use defineComponent() instead.
  Details: https://vuejs.org/api/general.html#definecomponent

it doesn't run. I'm getting:

vue.runtime.esm-bundler.js?fe26:1595 
        
       [Vue warn]: Component is missing template or render function. 
  at <App>