[jsscripting] Improve performance & reduce memory usage (#14113)

[jsscripting] Improve performance & reduce memory usage (#14113)

* [jsscripting] Share org.graalvm.polyglot.Engine across all OpenhabGraalJSScriptEngine instances

See https://github.com/oracle/graaljs/issues/121#issuecomment-880056648, it is not required to have one engine per GraalJSScriptEngine.

This might improve performance a bit on less powerful systems (Raspberry Pi) and decreases heap usage:
With 5 GraalJS UI scripts, heap usage is now below 100 MB. Before this change, it was over 100 MB.

* [jsscripting] Extend debug logging
* [jsscripting] Cache `@jsscripting-globals.js` across all engines

Signed-off-by: Florian Hotze <florianh_dev@icloud.com>