`globals` are not exposed in the Debugger

`global` Dart variables are not currently shown in the debugger.

@nshahan did some investigation and found we will likely need to request the `globals` for the current library. In Chrome DevTools, they are discoverable in a closure with the library name:

Begin with the debugger integration and the current-library scope request described in the issue; use the Chrome DevTools closure shown as the reference. The issue names no files or tests. Done means global Dart variables from the current library are visible in the debugger.

Written by the indexing model from the issue text.