Reland "Android testing use min sdk 19"

[utzcoz]

The latest Robolectric version, 4.11.x, removed the support for SDKs < 19 by following AndroidX strategy. Also following flutter/buildroot#750, and removing obsolete SDK checking in code to pass android_lint checking after bumping minSdk to 19 for testing target.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

[utzcoz]

I will learn how to integrate engine with flutter to ensure it doesn't break the flutter/flutter#138262 again.

[dnfield]

Are you interested in bumping this further to api 21? We've recently moved that up as the minimum elsewhere

[dnfield]

I'm going to close this since it's not passing tests right now and it never left draft status. Feel free to re-open if you plan to work on it again - or I might just do this to bump things to 21.

[utzcoz]

@dnfield Sorry for late response. I did't move this PR going because I didn't have enough time to test engine code with Flutter main repository's test code as the origin PR passed with Engine CI but failed with Flutter main repository's CI after checked-in. I can update this PR to bump related things to SDK 21 this weekend. I will reopen this PR and mark it as draft state.

[utzcoz]

Oh, looks like I don't have a permission to reopen it. I will resent one after updating.

[dnfield]

I ended up landing something like this for API 21 in #51032 (which had to get reverted because of one last framework test and then relanded). Thanks though!

[utzcoz]

Sorry, I will delay it to next weekend. @dnfield If you want to lan similar things, you can do it based on your pace.