JUnit Platform Console Standalone jars expose the platform version in
Specification-Version, while the bundled Jupiter engine version is stored
in Engine-Version-junit-jupiter. Prefer that Jupiter engine version for
junit-platform-console-standalone jars so JUnit 5 and JUnit 6 detection
uses the version of the test engine rather than the platform artifact.

Fall back to Specification-Version for the existing non-standalone cases
and leave annotation lookup/access restriction behavior unchanged.

Fixes: https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/2959