The current stable version of Flutter now requires API 21+, but most of our plugins have not been updated to reflect that, and still support API 19+. We have some tech debt related to older API support, and it would be good to find an clean out proactively (examples we've seen so far include flutter/packages#7876 and https://github.com/flutter/packages/pull/7874/files#r1802064758, but those are just things we've hit randomly so an audit would almost certainly turn up more)

This would look something like:

• Ensure that all the Android plugin implementation packages require Flutter 3.24+ (already true for many)
• Update them to minSdkVersion 21 (this should not be a breaking change as long as Flutter itself requires 21, but IIRC minSdkVersion can trigger behavior changes—although I don't remember if that's true at the level of our setting, or only at the level of the client app building them)
• Update the app-facing package README support table to say 21+ (some are probably quite stale; we don't currently have any checks in CI that these match the implementation package, which is a tracked issue).
• Scrub for any references to Build.VERSION that reference KITKAT or LOLLIPOP to see what's still needed in code.
• Delete or migrate any robolectric tests that reference api 20 or below. Tests that are verifying removed api behavior should be deleted, tests that verify apis work should be migrated.
• Ideally search any Java/Kotlin code for other references to KitKat, Lollipop, 19, 20, and 21 to try to catch things that aren't specifically Build references (like the second example above).