Add find_package wrapper

[zachcran]

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Originally part of NWChemEx/PluginPlay#375.

Description

This adds wrapper functions to CMake's find_package() that add a wrapper target in CMaize (nwx_wrap_target() and nwx_find_package()). This allows them to be added properly as dependencies for the main project target and appear properly in the installed <package>Config.cmake and <target>-target.cmake files.

TODOs

• Potentially rename the added functions to avoid implying that they are in the CMaize package (or migrate them to the CMaize package)
• License header?
• Validation of pairwise TARGETS argument to nwx_find_package
• Removed leftover commented-out code
• Add function-level documentation