Think about testing for debugger and/or webview

[NatKarmios]

Integration tests (e.g. cypress) may be possible, though we'd have be able to render the webview independently of VSCode functionality (or make all that functionality mockable).

Should the debugger be tested internally (i.e. within OCaml) or externally (i.e. with an external tool running the debugger)? Does this external tool exist?