Add unit testing for Slic ranks and rank counts

[bmhan12]

This PR:

• Adds testing for ranks and rank counts information in slic_macros_parallel unit tests.
• Remove std::ends from SLIC_ASSERT/SLIC_ASSERT_MSG/SLIC_CHECK/SLIC_CHECK_MSG macros that prevented Lumberjack from combining messages. When packing/unpacking messages for combining, std::ends does not play nice in std::string --> C-style string conversions. Trailing std::ends null character does not get included in the conversion, so output/rank Node's message (with std::ends null character) will always be different from the other nodes (nostd::ends null character), and as such no combining would take place.
  • Added check that messages are unique/combined for LumberjackStreams in unit tests.
  • Example Reproducer of behavior: https://godbolt.org/z/of9Y74sxz

Relates to #1410

[rhornung67]

Looks good. The only thought I have is that it may make the slic tests easier to understand if there were comments in the code indicating why the integer constants are chosen as they are; e.g., why N in something like (__LINE__ - N)

[kennyweiss]

Thanks @bmhan12 -- please don't forget to update the RELEASE_NOTES