Factor out encoding specific tests for json

Andrew Dunstan <andrew@dunslane.net>

Commit: b6363772fd5f07dcfff2b4869765705ac9633950
Author: Andrew Dunstan <andrew@dunslane.net>
Date: 2015-10-08T02:18:27Z
Releases: 9.6.0
Factor out encoding specific tests for json

This lets us remove the large alternative results files for the main
json and jsonb tests, which makes modifying those tests simpler for
committers and patch submitters.

Backpatch to 9.4 for jsonb and 9.3 for json.

Files