Collect changes to jpackage without a functional impact from the ongoing projects:

- Replace StringBuffer with StringBuilder where appropriate.

- LauncherBuilder: set reasonable defaults to "defaultIconResourceName" property; move defaultIconResourceName() from LauncherFromOptions.

- Make MacHelper.createRuntimeBundle() use PackageTest to create a runtime bundle. Will use DMG by default and optionally PKG packaging to create a runtime bundle.

- Remove redundat parameter from SetBuilder.build().

- Make JUnitUtils.assertArrayEquals() permit null-s.

- Add JPackageCommand.withToolProvider().

- Make some handy package-private methods in StandardBundlingOperation class public.

- IdentityWrapper: add wrapIdentity().

- Simplify DefaultBundlingEnvironment.createNativePackage().

- TKit: remove "throws IOException" from createDirectories(); Replace TKit.createDirectories() with Files.createDirectories() where directory clean-up is not used.