fix(compat): ensure proper handling of render function from SFC using Vue.extend (fix: #7766)

[LinusBorg]

This only affects compat mode

When a SFC uses Vue.extend() to define the component script, the compiler adds the render function as a property on the constructor, not the options object in .options

The same goes for internal properties added by the SFC compiler like __hmrId.

So when we create a vnode for such a component in compat mode, we have to re-assign these properties to the options object, which we then consequently use to create the actual component from.

If we don't do that, we get a template or render function missingerror.

fix: #7766

[ur92]

Thank for this fix, can you proceed to merge it?
We have a large Vue2/TS application that we want to migrate but currently we're stuck.
Thanks

[niksy]

Does this work on subcomponent extends? For example, I have component extended with Vue.extend, and another one which extends that component (Parent.extend). I’m still getting this warning after applying these changes. This worked in Vue 2.