Migrate JankStatsSample to Material 3 and update dependencies

* Migrate UI components, scaffold, and theme from Compose Material to Material 3.
* Update project dependencies including Kotlin, AGP, Compose BOM, JankStats, and Navigation3.
* Upgrade Java target and source compatibility to Java 21.
* Enable code minification (`isMinifyEnabled`) and resource shrinking (`isShrinkResources`) for release builds.
* Move `android.intent.action.MAIN` intent filter to `JankAggregatorActivity`.
* Remove unused dependencies and unused imports across the sample app.