[groovyscripting] For enum values do import static

[dilyanpalauzov]

Before this change

@groovy.transform.CompileStatic
def isOn(Object o) {
  return o == ON
}

caused:

[INFO ] [ort.loader.AbstractScriptFileWatcher] - (Re-)Loading script '/etc/openhab/automation/jsr223/t.groovy'
[ERROR] [ipt.internal.ScriptEngineManagerImpl] - Error during evaluation of script '/etc/openhab/automation/jsr223/t.groovy': org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
/etc/openhab/automation/jsr223/t.groovy: 3: [Static type checking] - The variable [ON] is undeclared.
 @ line 3, column 15.
     return o == ON
                 ^

1 error

[WARN ] [ort.loader.AbstractScriptFileWatcher] - Script loading error, ignoring file '/etc/openhab/automation/jsr223/t.groovy'

With the change, it prints:

[INFO ] [ort.loader.AbstractScriptFileWatcher] - (Re-)Loading script '/etc/openhab/automation/jsr223/t.groovy'
[DEBUG] [g.internal.GroovyScriptEngineFactory] - Added static import for DOWN
[DEBUG] [g.internal.GroovyScriptEngineFactory] - Added static import for PLAY
[DEBUG] [g.internal.GroovyScriptEngineFactory] - Added static import for ON
…