This commit uses standard files for libraries managed by the repackage
goal of the Maven plugin. Previously, only the name of the file was used
which could lead to duplicate libraries if the name of the target file
deviates from the default. This typically happens when the
`build.finalName` property is specified on a dependent module.

Note that the `maven-war-plugin` has an additional mechanism to customize
the file name structure of dependencies. This feature isn't supported by
the repackage goal so an explicit mention has been added in the
documentation.

Closes gh-7389