Deprecate -Xuse-k2 compiler flag in Gradle DSL

^KT-56239 Fixed

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinCommonCompilerOptions.kt

@@ -29,6 +29,7 @@ interface KotlinCommonCompilerOptions : org.jetbrains.kotlin.gradle.dsl.KotlinCo
      * Compile using experimental K2. K2 is a new compiler pipeline, no compatibility guarantees are yet provided
      * Default value: false
      */
+    @Deprecated(message = "Compiler flag -Xuse-k2 is deprecated; please use language version 2.0 instead", level = DeprecationLevel.WARNING)
     @get:org.gradle.api.tasks.Input
     val useK2: org.gradle.api.provider.Property<kotlin.Boolean>
 }

libraries/tools/kotlin-gradle-plugin-api/src/common/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinCommonOptions.kt

@@ -38,6 +38,7 @@ interface KotlinCommonOptions : org.jetbrains.kotlin.gradle.dsl.KotlinCommonTool
      * Compile using experimental K2. K2 is a new compiler pipeline, no compatibility guarantees are yet provided
      * Default value: false
      */
+    @Deprecated(message = "Compiler flag -Xuse-k2 is deprecated; please use language version 2.0 instead", level = DeprecationLevel.WARNING)
     var useK2: kotlin.Boolean
         get() = options.useK2.get()
         set(value) = options.useK2.set(value)

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinCommonCompilerOptionsDefault.kt

@@ -15,6 +15,7 @@ internal abstract class KotlinCommonCompilerOptionsDefault @javax.inject.Inject
     override val languageVersion: org.gradle.api.provider.Property<org.jetbrains.kotlin.gradle.dsl.KotlinVersion> =
         objectFactory.property(org.jetbrains.kotlin.gradle.dsl.KotlinVersion::class.java)
 
+    @Deprecated(message = "Compiler flag -Xuse-k2 is deprecated; please use language version 2.0 instead", level = DeprecationLevel.WARNING)
     override val useK2: org.gradle.api.provider.Property<kotlin.Boolean> =
         objectFactory.property(kotlin.Boolean::class.java).convention(false)