generic: check userspace handling of extreme timestamps

generic: check userspace handling of extreme timestamps

These two tests ensure we can store and retrieve timestamps on the
extremes of the date ranges supported by userspace, and the common
places where overflows can happen.

They differ from generic/402 in that they don't constrain the dates
tested to the range that the filesystem claims to support; we attempt
various things that /userspace/ can parse, and then check that the vfs
clamps and persists the values correctly.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>