Change get_ada_task_ptid parameter type

get_ada_task_ptid currently takes a 'long' as its 'thread' parameter
type.  However, on some platforms this is actually a pointer, and
using 'long' can sometimes end up with the value being sign-extended.
This sign extension can cause problems later, if the tid is then later
used as an address again.

This patch changes the parameter type to ULONGEST and updates all the
uses.  This approach preserves sign extension on the targets where it
is apparently intended, while avoiding it on others.

Co-Authored-By: John Baldwin <jhb@FreeBSD.org>