[FR] ProGuard Rules Shouldn't Ignore Warnings?

Hello fantastic Firebase folks,

It looks like all the ProGuard specs start by ignoring all warnings for the project that uses them, with `-ignorewarnings`.
(To reproduce, run `grep ignorewarnings external/firebase_cpp/libs/android/*.pro` from the latest release.)

This seems...dangerous, and is pretty heavily discouraged by the [ProGuard Manual](https://www.guardsquare.com/manual/configuration/usage) and disallowed in Bazel for similar reasons.

Is it necessary? (Things seemed to work fine without in a quick test) And if not necessary, would you be open to removing `-ignorewarnings`?

Cheers,
Chris

Start by running the issue's grep command against external/firebase_cpp/libs/android/*.pro and read each matching ProGuard rule. Compare the effect of removing -ignorewarnings with the ProGuard guidance linked in the issue and the reported quick test. Done means determining whether the flag is necessary and, if not, removing it consistently without breaking the Android release configuration.

Written by the indexing model from the issue text.