exfat: Implement fileattr_get for case sensitivity

exfat: Implement fileattr_get for case sensitivity

Report exFAT's case sensitivity behavior via the FS_XFLAG_CASEFOLD
flag. exFAT compares names through the volume's upcase table; in
practice that table folds case, and case is preserved at rest.

Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://github.com/exfatprogs/exfatprogs/issues/313
Link: https://patch.msgid.link/20260507-case-sensitivity-v14-4-e62cc8200435@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>