XFS on HaikuOS

Not major functionality changes or bug fixes anymore(All critical ones are already fixed 🙂) but a little bit of code refactoring.

- I found that every directory headers prefixes with Extent which is wrong, extents are basically what blockRun is in BFS so removed those prefix.

- Renamed Extent.cpp file to BlockDirectory.cpp since it implements block directory functionality.

#HaikuOS #xfs