Better handling of dependent extension's "enablement"

[marcdumais-work]

This extension (vscode-trace-server) is a companion to extension eclipse-cdt.vscode-trace-extension (Trace Viewer for VSCode) and depends on it.

At activation, this extension obtains a reference to the trace viewer's exported API object, and uses it to provide helper functionality. This work well normally, but there may be a corner-case that we should handle better: if/when the Trace Viewer extension becomes disabled, we probably should not use its API object any more, and if/when it becomes enabled again, we should obtain a fresh API object and redo the activation steps.

One scenario where the above might happen (to be confirmed) is when the Trace Viewer extension is updated to a new version.

As a starting point, here is how it seems the built-in vscode.github extension monitors the "enablement" of vscode.git-base it depends-on, and "refreshes" its API object when needed: