Expand TribitsExampleProject2 packages and TPLs (#299)

[bartlettroscoe]

This is driving #299

I need a deeper set of TPL dependencies to be able to test the next refactoring in TriBITS towards modern CMake targets (#299).

There are also a few related TriBITS changes part of this

• Add support for <tplName>_ALLOW_PACKAGE_PREFIND (commit 627917c1)
• tribits_tpl_find_include_dirs_and_libraries(): <tplName>_LIBRARY_NAMES cache var triggers lib finds (commit 3764e8b5)

NOTE: This PR looks intimidating with 47 changed files and over 900 lines changed but most of that is testing code and very simple code for the TPLs, TribitsExampleProject2, and TribitsExampleApp2.

This updated TribitsExampleProject2 is not quite done yet. I need to update support for optional upstream dependencies correctly to drive varied tests but this PR is a good start.

[bartlettroscoe]

Since no one is going to review this anytime soon, I will go ahead and merge. One can always do a post-merge review if needed.