Handle the static link in FrameDecorator

Handle the static link in FrameDecorator

A co-worker requested that the DAP scope for a nested function's frame
also show the variables from outer frames.  DAP doesn't directly
support this notion, so this patch arranges to put these variables
into the inner frames "Locals" scope.

I chose to do this only for DAP.  For CLI and MI, gdb currently does
not do this, so this preserves the behavior.

Note that an earlier patch (see commit 4a1311ba) removed some code
that seemed to do something similar.  However, that code did not
actually work.