This patch restricts the detection of moved members to be static members,
since only in this case we need to update qualified access to
them. The move of instance members will be either handled by rename or
we don't need to update anything at all.
Additionally, this patch introduces a sub-kind of type member diff item
called qualified replacement to describe the aforementioned case. However,
the migrator part has not started to honor this sub-kind yet.
rdar://32466196
Different from type hoist that moves global variables to static member
variables, we've also seen member variables being moved among different
types via apinotes. Swift-api-digester should be able to detect such
case so that migrator can handle them properly.
rdar://32466196
