* terminal,service: add way to see internal breakpoints

Now that Delve has internal breakpoints that survive for long periods
of time it will be useful to have an option to display them.

* proc,terminal,service: support stack watchpoints

Adds support for watchpoints on stack allocated variables.

When a stack variable is watched, in addition to the normal watchpoint
some support breakpoints are created:

- one breakpoint inside runtime.copystack, used to adjust the address
  of the watchpoint when the stack is resized
- one or more breakpoints used to detect when the stack variable goes
  out of scope, those are similar to the breakpoints set by StepOut.

Implements #279