This PR increases Android's `minSdkVersion` to 21.
There are two changes in this PR aside from simply increasing the number
from 19 to 21 everywhere.
First, tests using `flutter_gallery` fail without updating the
lockfiles. The changes in the PR are the results of running
`dev/tools/bin/generate_gradle_lockfiles.dart` on that app.
Second, from
[here](https://developer.android.com/build/multidex#mdex-pre-l):
> if your minSdkVersion is 21 or higher, multidex is enabled by default
and you don't need the multidex library.
As a result, the `multidex` option everywhere is obsolete. This PR
removes all logic and tests related to that option that I could find.
`Google testing` and `customer_tests` pass on this PR, so it seems like
this won't be too breaking if it is at all. If needed I'll give this
some time to bake in the framework before landing the flutter/engine
PRs.
Context: https://github.com/flutter/flutter/issues/138117,
https://github.com/flutter/flutter/issues/141277, b/319373605
* Revert "Mark last failing test after gradle update as flaky. (#91423)"
This reverts commit 46a52d03bd.
* Revert "fix android template for Gradle 7 (#91411)"
This reverts commit 51d06d537f.
* Revert "Add explicit version for mac and windows openjdk. (#91408)"
This reverts commit bf429f2771.
* Revert "Update the openjdk version used by linux android tests. (#91405)"
This reverts commit 2144ab8b45.
* Revert "Migrate to Gradle 7.0.2 / AGP 7.0.1 (#90642)"
This reverts commit b6459f9b63.
