Update Android Gradle Plugin to v3.2.1

[fractalwrench]

Goal

Update the AGP to v3.2+, to enable the SyntheticAccessor lint check. Synthetic accessors are generated when an inner class accesses a private method or field in its enclosing class, for example:

class Foo {
    private Bar bar;
    
    class Baz {
        Baz() {
            bar.toString(); // creates a synthetic accessor method to access bar
        }
    }
}

Changeset

• Update AGP to v3.2.1 (latest stable)
• Update Kotlin version to v1.3.10 (latest stable), as AGP v3.2.1 only supports Kotlin 1.2.71+
• Migrate to kotlin-stdlib dependency, as the deprecated kotlin-stdlib-jre artefact is not available in 1.3.10
• Adds baseline lint file to suppress existing issues for UnknownNullness and KotlinPropertyAccess.
• Relax visibility of methods/fields identified in SyntheticAccessor lint check to package-private, which removes 8 unnecessary methods 🎉

Tests

Ran existing test suites on CI

Discussion

Internal tickets have been created for addressing the pre-existing KotlinPropertyAccess and UnknownNullness checks in a separate PR.

[bengourley]

LGTM!