Prohibit JVM target 1.6

But still compile stdlib, reflect, kotlin.test and scripting runtimes
with JVM target 1.6 to simplify migration from Kotlin 1.6 to 1.7.

 #KT-45165 Fixed

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

@@ -24,4 +24,4 @@ interface KotlinCommonOptions  : org.jetbrains.kotlin.gradle.dsl.KotlinCommonToo
      * Default value: false
      */
      var useFir: kotlin.Boolean
-}
+}

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

@@ -12,8 +12,8 @@ interface KotlinJvmOptions  : org.jetbrains.kotlin.gradle.dsl.KotlinCommonOption
      var javaParameters: kotlin.Boolean
 
     /**
-     * Target version of the generated JVM bytecode (1.6 (DEPRECATED), 1.8, 9, 10, ..., 18), default is 1.8
-     * Possible values: "1.6", "1.8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18"
+     * Target version of the generated JVM bytecode (1.8, 9, 10, ..., 18), default is 1.8
+     * Possible values: "1.8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18"
      * Default value: null
      */
      var jvmTarget: kotlin.String?