Erik Lindahl authored Jun 16, 2023 and Andrey Alekseenko committed Jun 16, 2023

Let the XTC 32/64 bit format be based entirely on the
magic number in the header. This ensures files cannot be
inconsistent between header and atom-count, and it makes
it possible to test the new version without using files
of several gigabytes. All constants have also been
consolidated into a single header to ensure they cannot
diverge, and I have added internal checks that consistent
arguments are provided.

Refs #4628.