[CodeHealth] Remove uses of ListValue::Append in /components/wifi.

This CL removes uses of the overload that accepts a
std::unique_ptr<base::Value>. It attempts to modernize code where
feasible and uses base::Value::FromUniquePtrValue where it's not.

This CL was uploaded by git cl split.

R=agl@chromium.org

Bug: 1187097
Change-Id: I64287b5780c610986993b350b234f388409a88aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3626218
Commit-Queue: Adam Langley <agl@chromium.org>
Reviewed-by: Adam Langley <agl@chromium.org>
Auto-Submit: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#999136}