debugger: limit size of mirrored buffer
this commit makes output of debugger repl for buffer values similar to
one from util.inspect()
. Mirrored object is now returned as Buffer if
handle points to Buffer in debuggee. Also number of mirrored properties is
limited to INSPECT_MAX_BYTES. This will help significantly improve
speed of inspecting objects in debugger when one of the properties in
the tree is buffer. Most common case - inspecting http response object.