Debugger: Add "composite" watchers

Multiple expressions can be separated by semicolon,
and arrays allow index ranges given as [a..b] or
with strides [a.(s).b].

Change-Id: I0b7b4ee500a5f6f5027d777b0a1e8ee5a28a7cd5
Reviewed-by: Christian Stenger <christian.stenger@digia.com>