Add a ScriptEngine factory to ScriptTemplateConfigurer

[kl]

I'm using a the Graal.js engine with ScriptTemplateConfigurer with setSharedEngine(false) to enable thread safety.

Graal.js needs to be configured in order to enable Java interop, for example like this:

ScriptEngine engine = new ScriptEngineManager().getEngineByName("graal.js");
Bindings bindings = engine.getBindings(ScriptContext.ENGINE_SCOPE);
bindings.put("polyglot.js.allowHostAccess", true);
bindings.put("polyglot.js.allowHostClassLookup", true);

The problem is that it's not possible to create an engine instance, configure it and assign it to the ScriptTemplateConfigurer if setSharedEngine is false. In that case you can only set the engine name.

Would it be possible to add a ScriptEngine factory method to ScriptTemplateConfigurer so that it's possible to configure the thread local engine instances?