One of my pending work items for post-realm merge.
The lowest-level import task is no longer asynchronous, as we don't want
it to span multiple threads to allow easier interaction with realm.
Removing the `Task` spec simplifies a heap of usages.
Individual usages should decide whether they want to run the import
asynchronously, by either using an alternative override or spooling up a
thread themselves.
I've updated all cases where we should have been using
`GetDisplayString()` anyway, but left the `ToString()` implementations
in place for safety. They should probably be removed in the future.