pgsql: Re-add regression tests for ltree and intarray

Re-add regression tests for ltree and intarray

These tests have been removed by 906ea101d0d5, due to some of them being
unstable in the buildfarm with low max_stack_depth values. They are now
reworked so as they should be more portable.

The tests to cover the findoprnd() overflows use a balanced tree to
avoid using too much stack, per a suggestion and an investigation by Tom
Lane.

Note: This is initially applied only on HEAD; a backpatch will follow
should the buildfarm be fine with the situation.

Discussion: https://postgr.es/m/agZc6XecyE7E7fep@paquier.xyz
Backpatch-through: 14

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a6c430cabedca37eb0530a02d8d8f19e46aeec73

Modified Files
--------------
contrib/intarray/expected/_int.out | 15 +++++++++++++++
contrib/intarray/sql/_int.sql | 13 +++++++++++++
contrib/ltree/expected/ltree.out | 24 ++++++++++++++++++++++++
contrib/ltree/sql/ltree.sql | 20 ++++++++++++++++++++
4 files changed, 72 insertions(+)