#25246 Bump kotlin to 2.4.20; as most implementations are eol... Also, as a side effect; values() will be deprecated for kotlin enums, use entries instead from 1.9 onwards

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Summary by cubic

Bumps Kotlin to 2.4.20 across the generator, templates, and regenerated samples to replace end-of-life versions, and swaps deprecated values() for entries in enum codegen with no behavioral change.

• Updates Kotlin to 2.4.20 and the Gradle wrapper to 8.14.5 across templates and samples; jvm-volley also bumps the Android Gradle plugin to 8.5.2.
• Replaces deprecated kotlinOptions.jvmTarget with compilerOptions/JvmTarget in Gradle templates, using the kotlin { compilerOptions } block for spring-cloud.
• Pins kotlin-script-util to 1.8.22, drops the undefined javaslang.match.PatternsProcessor processor, reworks test compilation around K2JVMCompiler, and updates KotlinFileAssert for the new compiler API.
• Switches values() to entries in enum fromValue/forValue methods.