X-conjugate merge stage 1

[giltirn]

This is the first stage of the merge, containing the Xconjugate WilsonImpl and support machinery, instantiations of the Dirac operators and tests of the core technology, comparing to the G-parity operator in various ways. All tests pass on CPU machines, I will test again on Polaris/Perlmutter once all the merges into the staging branch have been completed.