This adds various customisations point in the app for security related
decisions. By default, these do nothing, but would be customised at the
app level via module replacement (so that no changes are needed here in the
SDK).
Fixes https://github.com/vector-im/element-web/issues/15350
TypeScript helpfully pointed me towards this dead code, which has been floating
around unused for a while. If we want to bring back ILAG in the future, we can
always revive it from history.
