Improve test coverage in bump.c

Improve test coverage in bump.c

There were no callers of BumpAllocLarge() in the regression tests, so
here we add a sort with a tuple large enough to use that path in bump.c.

Also, BumpStats() wasn't being called, so add a test to sysviews.sql to
call pg_backend_memory_contexts() while a bump context exists in the
backend.

Reported-by: Andres Freund
Discussion: https://postgr.es/m/20240414223305.m3i5eju6zylabvln@awork3.anarazel.de