When UpgradeJavaVersion bumps a project's Java version, the Kotlin compiler
keeps emitting bytecode at the older jvmTarget, leaving Kotlin classes at a
mismatched bytecode level. UpgradeJavaVersion now also runs a new
UpgradeKotlinJvmTargetVersion recipe that raises the Kotlin jvmTarget to match
the requested Java version across:

- kotlin-maven-plugin <jvmTarget> configuration
- Gradle Groovy and Kotlin DSL kotlinOptions/compilerOptions blocks
  (string and JvmTarget.JVM_X forms, including the jvmTarget.set(...) provider)

It never downgrades, and is a no-op for non-Kotlin projects. This flows through
the existing UpgradeBuildToJava*ForKotlin recipes, which delegate to
UpgradeJavaVersion.

Discovered while testing the Spring Boot 4 migration for Kotlin.

See moderneinc/customer-requests#2439

A string jvmTarget value is only valid in the legacy kotlinOptions DSL; in
compilerOptions jvmTarget is a Property<JvmTarget>, so a String assignment does
not compile. UpgradeKotlinJvmTargetVersion now distinguishes the enclosing
block: it bumps a string literal only inside kotlinOptions, and inside
compilerOptions acts only on the JvmTarget.JVM_X enum and jvmTarget.set(...)
provider forms. A stray string inside compilerOptions (already non-compiling
input) is left untouched for UseJvmTargetProviderSyntax to convert.