Java 8+ API desugaring support

[shubham1g5]

Summary

Enable desugaring to support Java 8 APIs like stream() for older devices (Android API 21 - 23)

Reference: https://developer.android.com/studio/write/java8-support#library-desugaring

Safety Assurance

• If the PR is high risk, "High Risk" label is set
• I have confidence that this PR will not introduce a regression for the reasons below
• Do we need to enhance manual QA test coverage ? If yes, "QA Note" label is set correctly

Safety story

Build level change to add support for Java 8+ APIs

[shubham1g5]

Causing tests to fail with -

java.lang.NoSuchMethodError: No static method toMap(Ljava/util/function/Function;Ljava/util/function/Function;)Lj$/util/stream/Collector; in class Lj$/util/stream/Collectors; or its super classes (declaration of 'j$.util.stream.Collectors' appears in /data/app/org.commcare.dalvik.test-rb9q8Vi83H-CwA9Zib9YlA==/base.apk:classes2.dex)

I inspected the release apk and java.util.stream.Collectors seems to be missing. I am not sure why. Going to leave it as it is for now and change the code to not use Stream Apis.