Function alloc_self_profile_query_strings 

pub fn alloc_self_profile_query_strings(tcx: TyCtxt<'_>)

All self-profiling events generated by the query engine use virtual StringIds for their event_id. This method makes all those virtual StringIds point to actual strings.

If we are recording only summary data, the ids will point to just the query names. If we are recording query keys too, we allocate the corresponding strings here.