fix(compiler-sfc): fix dynamic template ref in inline template

[Bigfish8]

fix #4866

[ygj6]

The problem with this approach is that we can't set the old value to null when unloading the ref.:worried:
eg: sfc.vuejs.org/
When you switch from HomeView to PostsView, Home_View is not set to null.

[Bigfish8]

Yes, you are right.
Notice that in this case,the component is keep-alive.I think the dynamic ref provides the way for users to access different component instance.Maybe it is the only condition?
If the user wants to access only one ref, ref is enough.Like this:
<component :is="currentTabComponent" ref="currentTabRef"></component>🤔