Support better representation of extension types in the debugger

[annagrin]

Parent: #49739

We don't currently show much useful information in the debugger for the extension types, as they don't exist at runtime.

Providing a useful experience would require bigger changes though the whole tooling ecosystem:

Design: describe how we present the static extension types to the user in the debugger UI
CFE (incremental compiler), frontend server, expression compiler worker: provide static types to the expression evaluation API.
vm service, vm, dwds: use the new API
DevTools: present static types and using new vm service API