Upgrade to Kotlin 2.2.0

[sdeleuze]

This commit leverages Kotlin 2.2 which is expected to be the new baseline for Spring Boot 4.0, so API and language versions are upgraded to KOTLIN_2_2 as well.

It also enables the -Xannotation-default-target=param-property compiler flag, mainly for test purpose, in order to avoid the related warnings and to use what will likely be the default in an upcoming Kotlin version short term. For more details see https://youtrack.jetbrains.com/issue/KT-73255.

KotlinPlatformJvmPlugin was a class from an old KMP plugin, deprecated for a long time and now removed. So its usage in PluginClasspathGradleBuild has been removed as well. @wilkinsona I think I don't see side effects after removing the offending line but please double check as I am not able to run some tests locally.

[wilkinsona]

Thanks, @sdeleuze. Would you mind taking a look at

spring-boot/spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/features/kotlin.adoc

Lines 15 to 28 in 5db3cac

	[[features.kotlin.requirements]]
	== Requirements
	Spring Boot requires at least Kotlin 2.1.x and manages a suitable Kotlin version through dependency management.
	To use Kotlin, `org.jetbrains.kotlin:kotlin-stdlib` and `org.jetbrains.kotlin:kotlin-reflect` must be present on the classpath.
	The `kotlin-stdlib` variants `kotlin-stdlib-jdk7` and `kotlin-stdlib-jdk8` can also be used.
	Since https://discuss.kotlinlang.org/t/classes-final-by-default/166[Kotlin classes are final by default], you are likely to want to configure {url-kotlin-docs}/compiler-plugins.html#spring-support[kotlin-spring] plugin in order to automatically open Spring-annotated classes so that they can be proxied.
	https://github.com/FasterXML/jackson-module-kotlin[Jackson's Kotlin module] is required for serializing / deserializing JSON data in Kotlin.
	It is automatically registered when found on the classpath.
	A warning message is logged if Jackson and Kotlin are present but the Jackson Kotlin module is not.
	TIP: These dependencies and plugins are provided by default if one bootstraps a Kotlin project on https://start.spring.io/#!language=kotlin[start.spring.io].

in the context of Kotlin 2.2 please? We can update the 2.1.x to 2.2.x for the minimum requirements, but I'm also wondering if there any other changes to be made there.

[sdeleuze]

Sure I will have a look and refine the documentation accordingly.

[sdeleuze]

Documentation update pushed.

[wilkinsona]

Thanks very much, @sdeleuze.