Introduce code quality tools for android.

[gengjiawen]

With the help of findbugs, PMD, we may find some problem early.

Maybe we can refer to: https://github.com/vanniktech/gradle-code-quality-tools-plugin.

cc @dulmandakh @hramos

[dulmandakh]

currently, I'm using https://developer.android.com/studio/write/lint and recent PRs to reduce errors/warnings detected by using lint.

it would be nice to start with very basic setup, and like commit must not increase error/warning count, otherwise CI fails.

[dulmandakh]

I found that there are many places where code just don't work due to use of newer APIs than 16 and crashes. I replaced some code from support library, but still having errors.

[dulmandakh]

another PR with lint error/warning fixes #23333. it's WIP.

[dulmandakh]

Note: ./gradlew :ReactAndroid:lint generates very useful report

[cpojer]

This issue was a discussion and we agreed that a PR should be sent. @gengjiawen please consider sending a PR with the fix but I'm gonna close the issue because on its own it isn't actionable.