miscellaneous improvements from the repair branch

[cmrschwarz]

This PR bundles some minor improvements that piled up on the repair branch:

• allow specifying default values for

  • additional_simd_template_parameter
  • additional_non_specialized_template_parameters

• fix the gather primitive making use of the new defaults and add testing for it

• fix unit test case generation for tests that specify an additional_simd_template_parameter

• improvements for tests helper functions

  • added integral_type_t
  • added rnd_init_bounded
  • fixed additional arg passing in test_memory_helper_t constructors

• proper 4 space indenting in generated files + other whitespace cleanups

[cmrschwarz]

reopening this to trigger the pipeline again. maybe we should change the github action workflow to make this less annoying?

[cmrschwarz]

should pass now, clang seems to have differing opinions on the interactions between parameter pack deduction and default arguments