Recurse into structs/arrays of one element when
assigning names.

Test incorporated into existing end-to-end debugger test,
hand-verified that it fails without this CL.

Fixes #19868

Revives CL 40010
Old-Change-Id: I0266e58af975fb64cfa17922be383b70f0a7ea96

Change-Id: I122ac2375931477769ec8d763607c1ec42d78a7f
Reviewed-on: https://go-review.googlesource.com/71731
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Keith Randall <khr@golang.org>