Relands #159756.

The original caused some stderr because

1. the configurable ndkVersion value that AGP provides used to be null by default.
2. Now it is not, instead it has a default value
3. integration_test doesn't actually use the NDK, but default for integration_test was higher that flutter.ndkVersion
4. We have code that checks if a plugin uses a higher ndk version and tells you to consider upgrading https://github.com/flutter/flutter/blob/master/packages/flutter_tools/gradle/src/main/groovy/flutter.groovy#L921

This reverts the revert, and then aligns integration_test's NDK version (which again, it doesn't actually use, so I'm not too concerned about the downgrade) with flutter.ndkVersion.

It also starts using the flutter.min/compile/ndkVersion values in integration_test, which was unrelated to the original pr. Can remove if you think it should land separately.

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, including Features we expect every widget to implement.
• I signed the CLA.
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• I followed the breaking change policy and added Data Driven Fixes where supported.
• All existing and new tests are passing.

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