Add unit testing for RRTMGP utilities

[peverwhee]

Tag name (The PR title should also include the tag name): n/a
Originator(s): peverwhee

Description (include issue title and the keyword ['closes', 'fixes', 'resolves'] and issue number):

Adds unit tests for the following RRTMGP utilities (and small scheme):

• schemes/rrtmgp/utils/rrtmgp_dry_static_energy_tendency.F90 (4 tests)
• schemes/rrtmgp/utils/calculate_net_heating.F90 (2 tests)
• schemes/rrtmgp/utils/radiation_tools.F90 (2 tests)
• schemes/rrtmgp/utils/radiation_utils.F90 (21 tests)
• schemes/rrtmgp/rrtmgp_sw_solar_var_setup.F90 (2 tests)

List all namelist files that were added or changed: n/a

List all files eliminated and why: n/a

List all files added and what they do:

A    test/unit-test/include/interpolate_stub.F90
- add stub so that radiation_tools.F90 will build

A    test/unit-test/tests/rrtmgp/CMakeLists.txt
A    test/unit-test/tests/rrtmgp/test_calculate_net_heating.pf
A    test/unit-test/tests/rrtmgp/test_radiation_tools.pf
A    test/unit-test/tests/rrtmgp/test_radiation_utils.pf
A    test/unit-test/tests/rrtmgp/test_rrtmgp_dry_static_energy_tendency.pf
A    test/unit-test/tests/rrtmgp/test_rrtmgp_sw_solar_var_setup.pf
- Add unit tests for RRTMGP

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

M    schemes/rrtmgp/utils/rrtmgp_dry_static_energy_tendency.F90
M    schemes/rrtmgp/utils/rrtmgp_dry_static_energy_tendency.meta
- change qrs_prime and qrl_prime to inout variables (bugfix)

M    test/unit-test/CMakeLists.txt
M    test/unit-test/tests/CMakeLists.txt
- add cmake infrastructure to see RRTMGP test directories

List all automated tests that failed, as well as an explanation for why they weren't fixed: n/a

Is this an answer-changing PR? If so, is it a new physics package, algorithm change, tuning change, etc? no

If yes to the above question, describe how this code was validated with the new/modified features: