Change locktype "speculative token" to "spectoken".

Change locktype "speculative token" to "spectoken".

It's just weird that this name wasn't chosen to look like an
identifier.  The suspicion that it wasn't thought about too
hard is reinforced by the fact that it wasn't documented in
the pg_locks view (until I did so, a day or two back).

Update, and add a comment reminding future adjusters of this
array to fix the docs too.

Do some desultory wordsmithing on various entries in the wait
events tables.

Discussion: https://postgr.es/m/24595.1589326879@sss.pgh.pa.us