Upgrade to Java 11

[laeubi]

The next Eclipse release would require Java 11 so it would be good to upgrade triquetrum as well

[cxbrooks]

I'm using JDK 14 with the target set to 1.8 and that seems to compile fine. There are those recent bugs, but I don't think that they are JDK issues.

If we compile with JDK 14 and run with target set to 1.8, is that sufficient to close this issue? Or, do we want to update releng/org.eclipse.triquetrum.repository/Triquetrum.product to not mention 1.8?

See also Bug #311 Update to Eclipse 2019-06 and Java 12

[laeubi]

Bundles + Java Compile version could simply be upgraded to java 11 so we can get benefits from java 11 features.