Previously, ltrimstr/rtrimstr would just let the input pass through for
non-string inputs or arguments.
That was happening because, they were leaking the errors returned by
startswith/endswith treating them as if they were jv_false().
The leak was resolved by #2977 for 1.7.1
This patch rewrites ltrimstr and rtrimstr in jq, and makes them not
ignore startswith and endswith errors anymore.
Emanuele Torre
1f1e619f4e