Patch download to work with symlinks (#736)

* Fix Download to work with symlinks

- Create SymlinkWalker
    * isPathSymbolic for whether any part of the path is symbolic, existing or not.
    * getRealPath for obtaining absolute, real path.
- Change Download to use SymlinkWalker
- Add in a new test for testing with symlinks

* Refactor
Switch to using Guava method for creating directories

* Fix import

* Alter test and fix arguments

* Forgot a def

* Fix method argument

* Change argument to child file

* Bump

src/main/java/net/fabricmc/loom/util/download/Download.java

@@ -24,6 +24,8 @@
 
 package net.fabricmc.loom.util.download;
 
+import static com.google.common.io.Files.createParentDirs;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -160,7 +162,7 @@ public class Download {
 		}
 
 		try {
-			Files.createDirectories(output.getParent());
+			createParentDirs(output.toFile());
 			Files.deleteIfExists(output);
 		} catch (IOException e) {
 			throw error(e, "Failed to prepare path for download");