Can't specify --min-api to d8

[ahumesky]

Bazel uses CompatDexBuilder while we remove the remaining dex support code:

https://github.com/bazelbuild/bazel/blob/d1ff8c2d15454444094f94765d4b57ce0232bb51/tools/android/BUILD.tools#L42

and CompatDexBuilder appears to hardcode the min api level:

https://r8.googlesource.com/r8/+/41d2ea5adff39b579b297219310199fd566e778b/src/main/java/com/android/tools/r8/compatdexbuilder/CompatDexBuilder.java#169

[ahumesky]

There's now an experimental attribute on android_binary called min_sdk_version available with 6.0.0 which will set the API level to use for dexing and desugaring:
https://github.com/bazelbuild/bazel/blob/534089ed10a253b31c499a284079f52a92bc0347/src/main/java/com/google/devtools/build/lib/rules/android/AndroidRuleClasses.java#L575-L583

It's experimental because the implementation can cause memory and caching issues, e.g. if two apps with different min_sdk_version values depends on the same android_library, then that library gets built twice.

I'll leave this issue open for now for folks to report any feedback.