Wait for included css to be fully loaded before instantiating a component / finishing the compilation #1694
Description
Use case:
A component needs to know how high it is. Right now it would schedule a promise / eventually use the new size event (see #1693). However, if we don't wait for nested CSS to be fully loaded before we instantiate a component the component has no way of knowing the right size.
The problem probably only appears for NativeShadowDomStrategy, as in the emulated mode we load nested stylesheets manually.