Support distinction between resolve and runtime requirements

[laeubi]

We have this report here in Tycho

• Dependency on junit-jupiter-api requires org.junit.platform.engine capability in target platform (despite effective directive) eclipse-tycho/tycho#5448

the problem is that currently P2 handles all required capabilities the same regardless of their effectivness.

For the build, Tycho likely only wants to consider effective:=resolve, while for install / execution also effective:=active should be used, and other maybe should be ignored at all.

To support this, we need to have a way to disable certain requirements as we already do for other purpose (e.g. source bundles) and do it like this:

1. no effective given or value is resolve we do as before
2. in other case we do similar to what source bundles do and add a org.eclipse.p2.effective.<name of directive> filter that evaluates to true by default but can be switched off by setting a context property