GROOVY-10663: Fixed issue in PackageHelperImpl#getPackageNames

[justinchuch]

Issue

PackageHelperImpl#getPackageNames would not be able to find and return
the package names if the package path or filename of the jar contains
plus signs due to the behavior of URLDecoder#decode.

URLDecoder#decode would decode the plus sign (i.e. +) as empty space, causing java.io.FileNotFoundException.

Reproduction

To reproduce the case, include a plus sign in the groovyVersion in the gradle.properties, e.g. 5.0.0+SNAPSHOT, run the PackageHelperImplTest, and testLoadAndGetPackagesEmpty would fail.

WARN [org.apache.groovy.groovysh.util.PackageHelperImpl] Error opening jar file : '/home/jus/repos/apache/groovy/build/libs/groovy-raw-5.0.0+SNAPSHOT.jar' : java.io.FileNotFoundException: /home/jus/repos/apache/groovy/build/libs/groovy-raw-5.0.0 SNAPSHOT.jar (No such file or directory)
...

Proposed fix

Use Paths.get(url.toURI()).toFile() instead of new File(URLDecoder.decode(url.file, 'UTF-8')).

[paulk-asert]

Looks good - merged!