[isabelle-dev] Java 15 ("zulu")

[Makarius]

With Isabelle/af54129abd9e we are using latest Java 15.

  * The provider is now azul.com (instead of adoptopenjdk.net): the "zulu"
releases cover more versions and more platforms, including current
arm64-darwin for macOS Big Sur on Apple Silicon.

  * Azul call Java 15 "MTS" (medium term support), in contrast to official
Java 11 "LTS" (long term support). Lets see how it works within the coming
weeks; in the worst case we can return to Java 11 from azul.com.

  * The Isabelle jdk component requires now 1.5 GB total, for all our 5
supported platforms.

  * The macOS app bundle requires 1.0 GB total, which includes 600 MB for
jdk-15 arm64-darwin and x86_64-darwin.

  * The full-screen problem on Big Sur is still open, see also
https://isabelle-dev.sketis.net/T35

  * The JTabbedPane problem on Big Sur is still open, see also
https://isabelle-dev.sketis.net/T36


If there are further Big Sur problems, we should at least collect them properly.


	Makarius