Update to TargetSdk 34, Compile with Java 21 and associated changes

[krc]

This updates just build- and manifest- related code, it does not touch Java application code.

Main point of changes:

• Set target API level to 34 (Android 14), minimum to 28 (Android 9)
• Compile with Java 21 instead of 8

Updates a few things to make that work and remove warnings from Android Studio:

• Update com.android.support to 28 (last version before the change to Jetpack/AndroidX)
• Update Gradle to 8.9
• Update Gradle repos (jcenter is gone)
• Update com.android.tools.build

Main Gradle/manifest syntax changes were:

compileSdkVersion -> compileSdk (etc) delete rootProject.buildDir -> delete rootProject.layout.buildDirectory added languageVersion = JavaLanguageVersion.of(21) added android:exported to android manifest added namespace for modules / removed package from android top level manifest

All per Android Studio warnings/tips

JUnit has not been updated, no API changes in the code have been made for newer versions, to keep this minimal.

Basic testing in Android Studio emulation: "Medium Phone API 35", "Pixel 4 API 30", "Small Phone API 28" Tested with USB attached phone Pixel 6a, Android 14/API 34 - Graphene OS

Options, "Help" and "About" screen all work, volume meter works - though I did not do any technical or math validation (but no logic code was touched, so). But the graph goes higher when sounds are louder, and acts differently in different modes.

[krc]

Went ahead and made this PR related to my issue #11 Feel free to use or not. If anything should be corrected before pulling, let me know!

Thanks again.