Doctool: lookup Java definitions

[abgruszecki]

The doctool should support referencing Java definitions with links, stdlib has got plenty of links like that.

[abgruszecki]

Alright, I've checked the issue out. It seems that we can look up some Java definitions. There's specifically a problem with java.util.Formatter, because all symbols for Formatter are considered absent. Judging from manual inspection, we can look up most Java definitions and cases like above are the exception. I've added some tests here: #11773.