[Feature Request] Option to export a modular jar

Currently when exporting a jar the `ModuleMainClass` attribute is not set in `module-info.class` so running a modular jar without manually specifying the main class is not possible. Additionally, there is no way to avoid generating a manifest when exporting a jar. This would be desirable so that a program which expects to be run as a module and depends on its module name not being null cannot be accidentally run with `java -jar`