[isabelle-dev] Java 17 LTS

[Makarius]

Official Java 17 LTS has been released on 15-Sep-2021, see also
https://docs.azul.com/core/zulu-openjdk/release-notes/17-ga

Isabelle/2a3fe3489bae uses the corresponding jdk-17+35 component. So far it
looks good (for Linux, Windows, macOS), but there might be some fine points
still to be addressed.

One such fine point is the bootstrap of old components in
Isabelle/41d009462d3c: both launch4j and jedit require the old Java 11 LTS
release, but end-users should not notice anything.


	Makarius