Show similar information to `Rendered fonts` from Chrome inspector

It'd be really nice to know what fonts actually got picked for a Flutter application. chrome has this:


In the inspector. It'd be great to have similar functionality in devtools.

/cc @jason-simmons @rusino
@kenzieschmoll

Start by reviewing Flutter DevTools' inspector and the Chrome inspector's “Rendered fonts” panel shown in the issue. Define how DevTools should expose the fonts selected for a Flutter application, then validate the feature in an inspector workflow; the issue names no target files or tests, so its scope needs maintainer agreement.

Written by the indexing model from the issue text.