Add OSGi test dependencies feature for target consumption

[laeubi]

Currently consuming OSGi test dependencies in PDE is a bit cumbersome, providing a feature for easier consumption would help users to adopt this powerful technology and enables advanced use-cases in PDE.

This is a split-up from

• Add OSGi test classpath support #1619

and could already be independently be used.

[github-actions]

Test Results

   765 files  ±0     765 suites  ±0   55m 38s ⏱️ - 3m 21s
 3 611 tests ±0   3 534 ✅  - 1   76 💤 ±0  1 ❌ +1 
10 833 runs  ±0  10 601 ✅  - 1  231 💤 ±0  1 ❌ +1 

For more details on these failures, see this check.

Results for commit d3389f9. ± Comparison against base commit 05d3333.