redact_arg_values throws a parse error on Options of type Vec

[BobEvans]

In Fuchsia's ffx tool, there is a declaration of an Option type, --config that can be a Vec.
from_args has no problem with invocations such as

ffx --config x --config y

However, redact_arg_values throws a parse error in ParseSlotValue that a duplicate value, y, was provided. It seems to be mistaking the Option type for a variant that has one value.

This is preventing the majority of analytics use cases from working for ffx.