Ext2FS: Replace Linux macros with homegrown Serenity-style definitions

[logkos]

This PR replaces ancient definitions for Ext2FS (which dates back to the first commit) with a custom implementation. The original header (which was borrowed from Linux) contained many unused elements, used Linux types and had an incompatible license. This change should resolve those issues and hopefully provide more flexibility when working with Ext2.

Currently a draft intended to gather consensus on the final approach.

And idk why but this makes serenity hang at console for no known reason. Any help here is welcome

[timschumi]

Regardless of the current build failure, there have been attempts to resolve the NIH-ness of the ext2 header in the past, but it was always deemed insufficient for getting rid of the license conflict. The fact that some comments in the reworked version are identical to the file that we are trying to get rid of should be enough of an indicator.

fwiw, I had started work on a from-scratch ext4 driver in the past (just using information from the Linux kernel wiki and documentation), but it's currently on ice (and therefore currently stuck at superblock parsing). I feel like that might be a more reliable way to resolve the issue.

[kleinesfilmroellchen]

+1, this is not something that seems worth solving right now, even though the C-ness of this header is really ugly.