Make DefaultClassPathResourceLoader handle URLs with format jar:file:/{JAR_PATH}!/{PREFIX}!/{RESOURCE} gracefully

[guillermocalvo]

Context:

Some class loaders, such as Spring Boot's LaunchedURLClassLoader which is used by Grails, resolve resources located inside a JAR file as jar:file:/{JAR_PATH}!/{PREFIX}!/{RESOURCE}.

For example:

• Resource application.yml
• Resolves as URL: jar:file:/path/to/the/jar/file.war!/WEB-INF/classes!/application.yml

When Micronaut's resource loader tries to get application.yml as a stream from the file system, it fails with:

DefaultClassPathResourceLoader : Error establishing whether path is a directory: /application.yml

java.nio.file.NoSuchFileException: /application.yml
  at jdk.zipfs/jdk.nio.zipfs.ZipFileSystem.newByteChannel(ZipFileSystem.java:702)
  at jdk.zipfs/jdk.nio.zipfs.ZipPath.newByteChannel(ZipPath.java:815)
  at jdk.zipfs/jdk.nio.zipfs.ZipFileSystemProvider.newByteChannel(ZipFileSystemProvider.java:252)
  at java.base/java.nio.file.Files.newByteChannel(Files.java:371)
  at java.base/java.nio.file.Files.newByteChannel(Files.java:422)
  at java.base/java.nio.file.Files.readAllBytes(Files.java:3206)
  at io.micronaut.core.io.scan.DefaultClassPathResourceLoader.getResourceAsStream(DefaultClassPathResourceLoader.java:126)
  ...

This PR makes sure these URLs hare handled gracefully if the resource is not found at the default location (ie. it will retrieve WEB-INF/classes/application.yml instead of application.yml).

Related issues:

• Error establishing whether path is a directory: /application.yml java.nio.file.NoSuchFileException grails/grails-core#12829
• Replace use of FileSystems.newFileSystem(URI) #7654

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