Fix plugins not loading when a ZipFS has already been opened for the current Jar

[shartte]

When VF is embedded in a Shadow Jar and that Shadow Jar is previously opened as a ZipFS, then this may happen when the plugins are initialized:

java.nio.file.FileSystemAlreadyExistsException
        at jdk.zipfs/jdk.nio.zipfs.ZipFileSystemProvider.newFileSystem(ZipFileSystemProvider.java:104)
        at java.base/java.nio.file.FileSystems.newFileSystem(FileSystems.java:339)
        at java.base/java.nio.file.FileSystems.newFileSystem(FileSystems.java:288)
        at org.jetbrains.java.decompiler.main.plugins.JarPluginLoader.init(JarPluginLoader.java:24)
        at org.jetbrains.java.decompiler.main.Init.init(Init.java:19)
        at org.jetbrains.java.decompiler.main.Fernflower.<clinit>(Fernflower.java:228)
        at org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler.<init>(ConsoleDecompiler.java:225)
        at org.jetbrains.java.decompiler.main.decompiler.ConsoleDecompiler.main(ConsoleDecompiler.java:178)
        at net.neoforged.snowblower.Generator.getDecompiledJar(Generator.java:711)
        at net.neoforged.snowblower.Generator.generate(Generator.java:532)
        at net.neoforged.snowblower.Generator.runInternal(Generator.java:365)
        at net.neoforged.snowblower.Generator.run(Generator.java:234)
        at net.neoforged.snowblower.Main.main(Main.java:130)

This PR aims to fix that by avoiding opening a URI based FS and instead tries to only use Path based FS.

[jaskarth]

Thanks for the fix!