Documentation: ext4: Document casefold and encrypt flags

Based on ext4(5) and fs/ext4/ext4.h.

For INCOMPAT_ENCRYPT, it's possible to create a new filesystem with that
flag without creating any encrypted inodes. ext4(5) says it adds
"support" but doesn't say whether anything's actually present like
COMPAT_RESIZE_INODE does.

Signed-off-by: Daniel Tang <[e-mail]>
Message-ID: <4506189.9SDvczpPoe@daniel-desktop3>
Signed-off-by: Theodore Ts'o <[e-mail]>

Documentation/filesystems/ext4/inodes.rst

···
      - Inode has inline data (EXT4_INLINE_DATA_FL).
    * - 0x20000000
      - Create children with the same project ID (EXT4_PROJINHERIT_FL).
+   * - 0x40000000
+     - Use case-insensitive lookups for directory contents (EXT4_CASEFOLD_FL).
    * - 0x80000000
      - Reserved for ext4 library (EXT4_RESERVED_FL).
    * -

Documentation/filesystems/ext4/super.rst

···
    * - 0x8000
      - Data in inode (INCOMPAT_INLINE_DATA).
    * - 0x10000
-     - Encrypted inodes are present on the filesystem. (INCOMPAT_ENCRYPT).
+     - Encrypted inodes can be present. (INCOMPAT_ENCRYPT).
+   * - 0x20000
+     - Directories can be marked case-insensitive. (INCOMPAT_CASEFOLD).
 
 .. _super_rocompat: