Installed neoforge server doesn't check for java version

[SAKO4444GODZ]

run.sh and run.bat both do not check for the version of the java binary that they will invoke. At least on Linux, this means that using Java 8 instead of 21 will cause the script to not fully execute (literally fails trying to use the user_jvm_args.txt).

Steps to reproduce:

set default java binary to the wrong version (eg. archlinux-java set openjdk-8)
install neoforge server (eg. the latest 1.21.4 beta)
./run.sh or ./run.bat
script errors; no server files generated

Possible fixes:
-Include java in server files (download while generating run.sh or include it in the jar)
-Have run.sh check for available java binaries
-Have run.sh download an appropriate java binary on first use, and use it each time
-Spit out an error if java version is inappropriate

(run.sh or run.bat) (first fix is stupid but works anyway)

If more information is needed feel free to reply