Improve contributor documentation for Android

[GregoryComer]

🚀 The feature, motivation and pitch

When trying to run Android tests, I ran into a few issues. It would be good to document the full process to run Android tests from a clean checkout, in order to help contributors.

Specifically, I had a bit of trouble with the following:

• I was missing the PTEs, and dug through the CI scripts to learn that I needed to run a CI script to generate them and then copy them to the build directory.
• I had difficultly getting the AAR bundled with the app. I was able to build it, but wasn't sure how to bundle it in a way that the tests can access. When running the tests, it would fail due to it being unable to find the AAR.

It would be great if we could include some information, either in CONTRIBUTING.md or in a readme under the Android test directory on the full process to run the tests locally from a clean checkout.

It would be great if we could go even further and integrate them seamlessly into the gradle build such that you could just run from Android Studio, but I'm not sure how practical that is. Even if we need to build the AAR separately, could we integrate the test PTE generation as a build step in gradle?

Alternatives

No response

Additional context

No response

RFC (Optional)

No response

cc @mergennachin @byjlw @kirklandsign @cbilgin

[kirklandsign]

I will update the docs

For missing PTE, ideally we can generate the PTE during gradle build.

[kirklandsign]

We need to build the AAR separately right now.

[kirklandsign]

We need to build the AAR separately right now.

#9985 is the first step to address this

[kirklandsign]

Trying to address the PTE and automation in #9989

[kirklandsign]

One more: #10174

[kirklandsign]

Hi @GregoryComer does these recent improvements help you with the development experience?