Update to jdk-21.0.11 --- second attempt!

[Makarius]

With Isabelle/895b651beabb we are on jdk-21.0.11, which alone is not very 
exciting: it is a routine update by Azul.

Two details are notable, though:

   (1) The Windows version has been built from sources, after applying a small 
patch (jdk-21.0.11/x86_64-windows.patch) to improve accessibility. This is the 
first time we build JDK from scratch for Isabelle. It turned out actually 
quite simple, much simpler than building VSCodium, for example. So this might 
encourage more patches in the future, also for other platforms.

   (2) The macOS version was broken in the first attempt, and instead of 
duplicating 1 GiB tar.gz / 1.7 GiB directory content, I have replaced the bad 
version non-monotonically. This can lead to confusion, if someone happened to 
run Admin/init or "isabelle components -a" within a time-window of approx. 
2-3h before 21:00 Royal Bavarian Time. In that case, local 
$HOME/.isabelle/contrib/jdk-21.0.11 and the corresponding .tar.gz need to be 
deleted, and Admin/init run again.


	Makarius