[1/2] Use proplist instead of #change record

This commit lays the groundwork by translating the record into a
proplist.  A follow-on commit will cause the RPC workers to send the
proplist instead of the record.

It also converts the 'complete' tuple into a tagged proplist.

BugzID: 24236
Merge '[1/2] Use proplist instead of #change record'

This merges 7199638e6adc76aa2563f70f66779d8d3fdb1211.