internal/fuzz: pass handle to temporary file instead of the path

internal/fuzz: pass handle to temporary file instead of the path

This CL partially reverts CL 297034. Inheritable handles are not
inherited by all workers thanks to using AdditionalInheritedHandles,
which explicitly specifies which handles to inherit by each worker.

This CL doesn't fix any bug, it's more of a cleanup, but also makes
the code more robust and more similar to its Unix counterpart.

Change-Id: I24c2d7f69dfb839a1aeb5858088d8f38b022f702
Reviewed-on: https://go-review.googlesource.com/c/go/+/506535
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>