Break out dimension interfaces for file i/o object

[peverwhee]

Tag name (required for release branches):
Originator(s): peverwhee

Description (include the issue title, and the keyword ['closes', 'fixes', 'resolves'] followed by the issue number):
Breaks out the dimension-specific interfaces for the file i/o object (instead of using assumed rank, which is a new-er fortran feature)
corresponding atmospheric_physics PR: ESCOMP/atmospheric_physics#248

Describe any changes made to build system: n/a

Describe any changes made to the namelist: n/a

List any changes to the defaults for the input datasets (e.g. boundary datasets): n/a

List all files eliminated and why: n/a

List all files added and what they do: n/a

List all existing files that have been modified, and describe the changes:
(Helpful git command: git diff --name-status development...<your_branch_name>)
M src/physics/utils/pio_reader.F90

• break out extra dimension interfaces

If there are new failures (compared to the test/existing-test-failures.txt file),
have them OK'd by the gatekeeper, note them here, and add them to the file.
If there are baseline differences, include the test and the reason for the
diff. What is the nature of the change? Roundoff?

derecho/intel/aux_sima: all pass

derecho/gnu/aux_sima: all pass

The file_io_test test suite also runs successfully.

If this changes climate describe any run(s) done to evaluate the new
climate in enough detail that it(they) could be reproduced:

CAM-SIMA date used for the baseline comparison tests if different than latest:

[nusbaume]

Thanks again @peverwhee!

[mwaxmonsky]

Thanks for tackling this @peverwhee!