Add Android-JAR plugin to kx-coroutines-android

[wojtek-kalicinski]

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The Android-JAR plugin works based on the following principles:

• can be added to a project with both plugins: java-library and maven-publish
• creates 2 new configurations: aarRuntime and aarApi with attributes that are requested by Android Gradle plugins
• creates .aar artifacts for these configurations that pull in the regular .jar and additional files specified through extension
• provides extension for configuring required values for the AAR manifest: minSdk and namespace
• adds the AAR configurations/artifacts to the maven publication throught the components.java

As a result, we'll be able to continue shipping JARs to JVM clients (e.g. host side tests) and AAR to Android clients through the resulting Gradle module metadata.

In the future, I'm hoping to ship this plugin as part of Android Gradle plugins (com.android.) and this code could then be removed.