Add support for configuring `--system` using `java_package_configuration`

Also use `cfg = "target"` for `java_toolchain.package_configuration` to ensure `java_package_configuration.system` is built in the target config, and do the exec transition later for `java_package_configuration.data` (which we do want in the exec config). The system needs to match the target Java language configuration, the data is an exec dependency used at built-time.

PiperOrigin-RevId: 684478368
Change-Id: Iaa2020525b204cf9eabc0cd1830cb3bdc40da683