Make development more-friendly for TypeScript 6/7 (#4272)

* Update devcontainer.

* Switch module settings, turn on `noEmit`, and drop explicit `lib`.

* module->namespace

* Switch troublesome packages to use `import = require()` syntax.

* Remove unnecessary declaration file.

* Drop DOM declarations.

* Fix up errors from more restrictive signature of `vscode.l10n.t`.

* Fix chat-lib script - we no longer have that stray file.

* Update dependencies.