Refactor gradle option generation mechanism

Ensure there's a statically checked dependency on LanguageVersion and
JvmTarget, so that this information is updated automatically once a new
language version or a JVM target is added

compiler/testData/cli/js/jsHelp.out

@@ -6,7 +6,7 @@ where possible options include:
   -source-map                Generate source map
   -meta-info                 Generate metadata
   -kjsm                      Generate kjsm-files (for creating libraries)
-  -target { v5 }             Generate JS files for specific ECMA version)
+  -target { v5 }             Generate JS files for specific ECMA version
   -module-kind { plain, amd, commonjs, umd }
                              Kind of a module generated by compiler
   -main {call,noCall}        Whether a main function should be called