XACT_EVENT for 'commit prepared'

Hi hackers,

I found that in enum XactEvent, there is 'XACT_EVENT_PREPARE' for
'prepare transaction', but there is no event for 'commit prepared' or
'rollback prepared'.

For the following SQL:
------------------------------------------------
begin;
create table test(a int);
PREPARE TRANSACTION 'foo';
rollback prepared 'foo';
-------------------------------------------------
When executing ' rollback prepared 'foo'; ', I expected to get
'XACT_EVENT_ABORT', but actually,
the event type is 'XACT_EVENT_COMMIT'.

I think XACT_EVENT_COMMIT_PREPARED and XACT_EVENT_ROLLBACK_PREPARED can be
added in function 'FinishPreparedTransaction'

I'm confused why there are no related events for them.