Update the `Repackager` class so that an additional `classpath.idx` file
is written into the jar that provides the original order of the
classpath. The `JarLauncher` class now uses this file when running as
an exploded archive to ensure that the classpath order is the same as
when running from the far jar.

Closes gh-9128
Co-authored-by: Phillip Webb <pwebb@pivotal.io>