[Java] Upgrade Language Server

[dmelikhov]

Please, upgrade the language server Java is using.

The eclipse.jdt.ls version currently in use is 0.21, which is very very old.

It's so old that it doesn't even support Java 11 as Maven target.
(support was added in 0.26: https://github.com/eclipse/eclipse.jdt.ls/blob/master/CHANGELOG.md)

I suggest upgrading it to the latest version - 0.65, yet I'm not sure about all the breaking changes.