Merge branch 'brobey/mpas-ocean/openacc-newextendsplit' (PR #4954)

Reimplementation of extensions to OpenACC region in time integration split routine

Reimplementation of extensions to OpenACC region to encompass the entire
if blocks for the split explicit step:
* Extending the OpenACC region to encompass all of the large iteration
  if block
* Extending OpenACC region outside the if splitExplicitStep blocks
* Fixing loop in diagnostic solve to run on GPU
These changes are separate and independent from the addition of the
OpenACC top of the split routine changes.

[BFB]