Warn if LOCKTAG_TUPLE is held at commit, under debug_assertions.
The current use always releases this locktag. A planned use will
continue that intent. It will involve more areas of code, making unlock
omissions easier. Warn under debug_assertions, like we do for various
resource leaks. Back-patch to v12 (all supported versions), the plan
for the commit of the new use.
Reviewed by Heikki Linnakangas.
Discussion: https://postgr.es/m/
20240512232923.aa.nmisch@google.com