CMake: Make checked_find_package able to prefer configs (#2984)
CMake: Make checked_find_package able to prefer configs (#2984)

Both global and per-package controls have been added to our
checked_find_package cmake function, to cause it to first check for
an exported config for the dependency, and only if not found, revert
to potentially using a FindPackage.cmake module.

This reflects our general leaning toward assuming that a package that
exports a cmake config probably does a better job of it than we would
do writing a Find module for it.
OpenImageIO/oiio,lgritz/oiio,lgritz/oiio,OpenImageIO/oiio,lgritz/oiio,OpenImageIO/oiio,OpenImageIO/oiio,lgritz/oiio