Module finder incorrectly assumes default file system path-separator character

The module finder implementation incorrectly uses the path-separator
character from the default file system, when mapping the relative path
of an entry in an exploded module to a package name. This causes
problems on Windows [*] when using a module finder with a custom file
system that has a path-separator character that differs from that of the
default file system, e.g. the zip file system (which uses '/',
rather than '\' ).

[*]
java.lang.module.FindException: Error reading module: /m2
        at java.base/jdk.internal.module.ModulePath.readModule(ModulePath.java:350)
        at java.base/jdk.internal.module.ModulePath.scanDirectory(ModulePath.java:284)
        at java.base/jdk.internal.module.ModulePath.scan(ModulePath.java:232)
        at java.base/jdk.internal.module.ModulePath.scanNextEntry(ModulePath.java:190)
        at java.base/jdk.internal.module.ModulePath.findAll(ModulePath.java:166)
        at ModulesInCustomFileSystem.listAllModules(ModulesInCustomFileSystem.java:108)
        at ModulesInCustomFileSystem.testZipFileSystem(ModulesInCustomFileSystem.java:97)
        at ModulesInCustomFileSystem.testExplodedModulesInZipFileSystem(ModulesInCustomFileSystem.java:68)
        at ...
Caused by: java.lang.module.InvalidModuleDescriptorException: Package q.r not found in module
        at java.base/jdk.internal.module.ModuleInfo.invalidModuleDescriptor(ModuleInfo.java:1212)
        at java.base/jdk.internal.module.ModuleInfo.doRead(ModuleInfo.java:330)
        at java.base/jdk.internal.module.ModuleInfo.read(ModuleInfo.java:129)
        at java.base/jdk.internal.module.ModulePath.readExplodedModule(ModulePath.java:689)
        at java.base/jdk.internal.module.ModulePath.readModule(ModulePath.java:320)
        ... 36 more