x/debug: support getting values of map type.

Calling program.Value to get the value of a map returns a program.Map
struct, which contains the type identifier, address, and length of the

Users can then call program.MapElement to get variable references for
each element's key and value.  The values of those variables can be
found by calling program.Value again.

Change-Id: Ib9d5d9d5ca00a121e4b13b16c3a637c6dc168119
Reviewed-on: https://go-review.googlesource.com/13657
Reviewed-by: Rob Pike <r@golang.org>
9 files changed