Convert packages/flutter_tools/gradle/src/main/kotlin_scripts/dependency_version_checker.gradle.kts from Kotlin script to Kotlin source, including renaming and moving to packages/flutter_tools/gradle/src/main/kotlin/DependencyVersionChecker.kt.

We do some fragile reflection in this script that will likely need to be removed as part of the conversion, because it depends on using Groovy's dynamic dispatch. From a brief look, it should now be possible to do something like

import com.android.build.api.AndroidPluginVersion

...

AndroidPluginVersion.getCurrent() // The AGP version
com.android.build.gradle.internal.utils.getKotlinAndroidPluginVersion(project) // The Kotlin version
project.gradle.gradleVersion // The Gradle version
JavaVersion.current() // The Java version

Though pointing at a method that has "internal" as part of its class path is suspicious! Weird that it is possible!

Then modify it's usage in flutter.groovy to no longer be applied as a script, just used as a class.