Remove placeholder jshell jdk8 module

[mbien]

• remove lib.nbjshell module
• rename lib.nbjshell9 to lib.nbjshell, effectively replacing the original placeholder module
• bump module requirements to JDK 11

implemented analog to #7677

wip

[lahodaj]

I think this will be a good cleanup.

[mbien]

@lahodaj originally I only intended to replace lib.nbjshell with lib.nbjshell9, but it turned out that both modules can likely be removed.

while testing I noticed that jshell doesn't work if NB runtime JDK < configured jshell JDK. I am not sure if this was a requirement or not. Thats why I set it back to draft. (this is the case in NB 25 already, with or without this PR. If NB runs on JDK 17 it can't run jshell on 21.

[matthiasblaesing]

The cross-jdk access indeed seems to be problematic. NB running on JDK 23 can use target JDK 23 and 21, but not 17. Running this by hand shows the problem:

matthias@enterprise:~$ /usr/lib/jvm/java-17-openjdk-amd64/bin/java -classpath /home/matthias/bin/netbeans-dev/java/modules/ext/nb-mod-jshell-probe.jar: -Xrunjdwp:transport=dt_socket,address=localhost:53633,suspend=y,includevirtualthreads=n org.netbeans.lib.jshell.agent.AgentWorker 35645
ERROR: JDWP option syntax error: -agentlib:jdwp=transport=dt_socket,address=localhost:53633,suspend=y,includevirtualthreads=n
matthias@enterprise:~$

The new parameter includevirtualthreads breaks the connection setup.

In the opposite direction I see a problem when running on JDK 17 and choosing JDK 21 as platform. If I read ShellSession.java correctly, the code asks the runtime JDK to create a javac with target of the target platform. This must go wrong.

So I think this is not a regression, just a feature, that is broken when not used in default configuration (target JDK != runtime JDK).