When a fatal Glk error is raised, give opportunity to the VM to present a stack trace

[curiousdannii]

There's now no good way for a VM stack trace to be shown when a fatal Glk error is raised. This would require basically a whole ecosystem rethink, but there are a few possible ways we could do this:

1. Have GlkApi ask the VM for a stack trace
2. Don't display any errors directly from GlkApi, but throw an error, require the VM to catch it, and then show the error itself.