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