Add links to other public javadoc pages

[ST-DDT]

Adds links to other public javadoc pages.

This has the following benefits

• Replaces fqcn with links to the official docs, which are usually more useful then just the name.
• Allows creating proper hierarchies for custom implementations (?)
• Derive some javadocs from the external parents (?)

Limitations

• Does not work with java 11
  • This might be caused by a bad configuration of grpc-java's javadocs (Cannot link to javadoc from jdk11's javadoc tool grpc/grpc.github.io#801)

TBD/TBC

• Do we want the external links at all?
• Currently the javadoc links for spring reference a specific version of spring which is not bound to the dependency version. Is it possible to somehow reference the variables instead?
• Need to check which version of the spring-framework is actually used in the referenced spring-boot lib.

[yidongnan]

Do we want the external links at all?

I think this is ok.

Currently the javadoc links for spring reference a specific version of spring which is not bound to the dependency version. Is it possible to somehow reference the variables instead?
Need to check which version of the spring-framework is actually used in the referenced spring-boot lib.

We can read the version of the dependency from the dependency manager

[ST-DDT]

Currently the javadoc links for spring reference a specific version of spring which is not bound to the dependency version. Is it possible to somehow reference the variables instead?
Need to check which version of the spring-framework is actually used in the referenced spring-boot lib.

We can read the version of the dependency from the dependency manager

Do you know how to do this? Does it work like this?