chore: update to Java 17 and Gradle 8.4

[lemonderon]

What does this change?

Most of the first-party flutter plugins (like package_info_plus, device_info_plus, connectivity_plus) now require the usage of Java 17, compileSDK 34 and Gradle 8.4.

Having a flutter app with ua_client_hints: 1.2.2 in pubspec and with the following build.gradle config

    compileOptions {
        sourceCompatibility JavaVersion.VERSION_17
        targetCompatibility JavaVersion.VERSION_17
    }

    kotlin {
        jvmToolchain(17)
    }

results in

Execution failed for task ':ua_client_hints:compileDebugKotlin'.
> 'compileDebugJavaWithJavac' task (current target is 1.8) and 'compileDebugKotlin' task (current target is 17) jvm target compatibility should be set to the same Java version.

Updating the build.gradle resolved compilation issue for me and I did not notice any compilation/package behaviour changes.