Move DateTimeEdit into libshared

BInvoker methods are now used, and input-handling is also tweaked.

Change-Id: I120cca8df9f11c11aac80911108d62fb49488f8f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4927
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>