Change <PACKAGE>_DIR to <PACKAGE>_ROOT in SetupSeracThirdParty.cmake

[ebchin]

I'm adding Enzyme as a TPL and I've noticed that the ENZYME_DIR defined in the host config file does not match the directory found by find_dependency() for my install. Looking at the search order, it looks like PATHS "${ENZYME_DIR}" is the 4th option used to find this package. Does it make sense to switch our TPLs in SetupSeracThirdParty.cmake to use <PACKAGE>_ROOT instead, which appears to be the first option?

[btalamini]

Pinging @chapman39 and @white238