Closes: roc-streaming#72, roc-streaming#112, roc-streaming#116, roc-streaming#106, roc-streaming#107, roc-streaming#105

- Update requirements:
    for build: JDK 17+
    for running: JRE 8+
    Android SDK: 31+ (Android 12)
    Android API: 29+ (Android 10)

- Bump gradle version and fix build on recent JDK versions

- CI:
    bump actions versions
    cleanup
    test JDK 21 and JDK 17
    switch to android-actions/setup-android
    downgrade roc-toolkit from master to v0.2.6
    automatically select best roc-toolkit git tag for release AAR

- README:
    document version requirements
    cleanup build & devel instructions
    document where versions are hard-coded

- Gradle:
    use io.freefair.android-lombok on Android
    run delombok before javadoc
    disable javadoc warnings
    switch from "maven" to "maven-publish" plugin
    fix cmake warnings due to incorrect invocation

- Sources:
    fix javadoc errors
    exclude gradle code from javadoc