Use `EventName` for `TransactionEvent`

[PhilippGackstatter]

After the VM upgrade to 0.19 (#2042), we can provide EventNames for TransactionEvents. Currently we have:

pub enum TransactionEvent {
    AccountBeforeForeignLoad = ACCOUNT_BEFORE_FOREIGN_LOAD,
}

where ACCOUNT_BEFORE_FOREIGN_LOAD is a u64, essentially an EventId, generated in build.rs.

With VM 0.19 we still need a way to map an EventId to a TransactionEvent so we can implement TransactionEvent::try_from(event_id). But, additionally, we can implement TransactionEvent::event_name, e.g.:

// Generated by build.rs next to ACCOUNT_BEFORE_FOREIGN_LOAD.
pub const ACCOUNT_BEFORE_FOREIGN_LOAD_EVENT_NAME: EventName =
    EventName::new("miden::account::before_foreign_load");

impl TransactionEvent {
    pub fn event_name(&self) -> &EventName {
        match self {
            TransactionEvent::AccountBeforeForeignLoad => &ACCOUNT_BEFORE_FOREIGN_LOAD_EVENT_NAME,
            // ...
        }
    }
}

The main benefit is that we can then implement BaseHost::resolve_event for TransactionExecutorHost roughly like this:

fn resolve_event(&self, event_id: EventId) -> Option<&EventName> {
    let event_name = self.base_host.stdlib_handlers().resolve_event(event_id);
    if event_name.is_some() {
        return event_name;
    }

    TransactionEvent::try_from(event_id).map(|event| event.event_name()).ok()
}

As part of this, we can check if having the EVENT_NAME_LUT still makes sense. At first glance, it looks like its functionality is covered by BaseHost::resolve_event and if so, we can probably remove it.