Replace dCache's 'DirectoryStream' with Java's 'DirectoryStream'

[LukasMansour]

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Motivation: Closes #3821

Modification: Replaces dCache's old 'DirectoryStream' with Java's 'DirectoryStream'.

Removing dCache's old DirectoryStream results in some empty IOException catch-blocks that shouldn't be throwable...

Result: The returned Streams of DirectoryEntry are now always a type of JDK's NIO DirectoryStream<DirectoryEntry>, dCache's custom DirectoryStream is removed. There are some empty (throw RuntimeException) blocks for IOExceptions that are not throwable. They appear since the JDK Interface Closable defines a close()-method with an IOException Throwable. and DirectoryStream inherits from Closable.

Signed-off-by: Lukas Mansour [email protected]