bug(top-app-bar): foundation should be destroyed and reinitialized on variant change

[mgr34]

When the <TopAppBar/>'s variant changes the foundation is not reinitialized. For example, if mounted with fixed=true and an update changes this to fixed=false the component should destroy() the present foundation (an instanceof MDCFixedTopAppBarFoundation) and reinitialize a plain MDCTopAppBarFoundation. Otherwise upon scroll mdc-top-app-bar--fixed-scrolled className will be added to the <TopAppBar/>.

Note: I believe I have a PR nearly complete. New to Screenshot testing. Had some issues figuring out setting up the environment (see: discord ).

[moog16]

@mgr34 Ya we do need something to switch if that is your intention. This is similar to the Drawer. Please see this 36e6316.

I think the same principles can be applied to top app bar.