[GeoMechanicsApplication] Separate test suites to improve compilation

[rfaasse]

📝 Description
This PR puts the suite without kernel in a separate file. This means that any test that only includes the new file, (implicitly) includes a lot less headers. This has two advantages:

• First of all, the compilation unit for that specific test compiles more quickly, as less headers are included in the compilation unit.
• Second, the compilation unit for that specific test is dependent on a smaller number of other headers, meaning it will need to be recompiled less often (as that's only triggered when there are changes in the respective cpp file, or any (indirectly) included headers.

In this PR the separation and one example is shown. For this specific example the compile times are as follows:

before:
38279ms applications/GeoMechanicsApplication/CMakeFiles/KratosGeoMechanicsCoreTest.dir/tests/cpp_tests/custom_conditions/test_axisymmetric_U_Pw_normal_face_load_condition.cpp.obj

after:
28510ms applications/GeoMechanicsApplication/CMakeFiles/KratosGeoMechanicsCoreTest.dir/tests/cpp_tests/custom_conditions/test_axisymmetric_U_Pw_normal_face_load_condition.cpp.obj

Of course due to parallel building this doesn't mean we win 10 seconds for each test, but it is significant and also helps rebuilding less often in the first place (winning even more time).

By slowly converting tests in the same fashion as this example, we'll improve include health and build times

[rfaasse]

I didn't mean for this PR to be reviewed yet (but created it without making it a draft, my mistake), so please wait until I put it as ready for review again 👍

[markelov208]

Hi Richard, thank you for speeding up the compilation. It looks that we should use more gtests instead of KRATOS macros, right?