pgsql: Convert contrib/ltree's input functions to report errors softly

Convert contrib/ltree's input functions to report errors softly

Reviewed by Tom Lane and Amul Sul

Discussion: /messages/by-id/49e598c2-cfe8-0928-b6fb-d0cc51aab626@dunslane.net

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7a05425d96742acff5ebfacf307711385c88429b

Modified Files
--------------
contrib/ltree/expected/ltree.out | 25 ++++++++++++++
contrib/ltree/ltree_io.c | 72 +++++++++++++++++++++++---------------
contrib/ltree/ltxtquery_io.c | 75 ++++++++++++++++++++++++++++------------
contrib/ltree/sql/ltree.sql | 15 ++++++++
4 files changed, 137 insertions(+), 50 deletions(-)