Fix issue with resource files not loaded on Ubuntu Linux

[ghost]

On Ubuntu Linux the attempt to enumerate DAO block files in a JAR resource directory fails.

See #5894 (comment)

All the block data is then downloaded from the seednodes.

This PR does the enumeration using nio.File.FileSystem so that block files in resources can be used.

[ripcurlx]

toString is not necessary.

Suggested change

	log.info("No files in directory. {}", dirUrl.toString());
	log.info("No files in directory. {}", dirUrl);

[ripcurlx]

Doesn't work now on macOS unfortunately

java.lang.IllegalArgumentException: Path component should be '/'
	at java.base/sun.nio.fs.UnixFileSystemProvider.checkUri(UnixFileSystemProvider.java:81)
	at java.base/sun.nio.fs.UnixFileSystemProvider.newFileSystem(UnixFileSystemProvider.java:90)
	at java.base/java.nio.file.FileSystems.newFileSystem(FileSystems.java:338)
	at java.base/java.nio.file.FileSystems.newFileSystem(FileSystems.java:287)
	at bisq.core.dao.state.storage.BsqBlocksStorageService.copyFromResources(BsqBlocksStorageService.java:131)
	at bisq.core.dao.state.storage.DaoStateStorageService.lambda$readFromResources$4(DaoStateStorageService.java:119)
	at java.base/java.lang.Thread.run(Thread.java:832)

[ripcurlx]

NACK - #5898 (comment)

[stejbac]

I was debugging the same issue on Windows a couple of days ago, caused by the expression new File(dirUrl.toUri()). I ended up adapting the following method from StackOverflow, which seems to work:

https://stackoverflow.com/questions/3923129/get-a-list-of-resources-from-classpath-directory/48190582#48190582

It looks like you have to use two different code paths to list the resource directory, depending on the environment.

(I created a draft patch for the fix, but never got round to creating a PR out of it. The foreach loop to do the copying needs modifying to work on Windows as well, just like in this PR.)

[ghost]

@stejbac Looks like we were both debugging the same issue. As this one does not work for MacOs, can you make your PR?

[stejbac]

@jmacxx OK, sure.

[chimp1984]

@stejbac Ah great that you tackled that as well. Could we extract the handling in a FileUtil class to make it re-usable. A pity that simple filehandling from resources is such a mess in java...
We have verious other loadFromResource calls. Maybe worth to re-check if there are issues as well.