Simplify the testing types

[thoasm]

Add template-type functions to combine and merge type lists. As a result, the GINKGO_DPCPP_SINGLE_MODE only needs to be present once.

Additionally, change the typen name ValueAndIndexType to ComplexAndPODTypes (because gko::size_type is not an IndexType).

TODO:

• [x] Add documentation to the type helper
• [x] go through all existing tests and use the wrapper in all cases we define types on our own (example: CB-Gmres)

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.25%. Comparing base (19269b6) to head (a881a3d). Report is 8 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1594 +/- ## =========================================== + Coverage 89.96% 90.25% +0.28% =========================================== Files 763 764 +1 Lines 62877 62907 +30 =========================================== + Hits 56570 56779 +209 + Misses 6307 6128 -179 ```

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