Change 'jvmTarget' backing property visibility to internal.

Allows to check if this property was updated by the user or not.

^KT-45611 In Progress
^KT-43095 In Progress

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/GradleOption.kt

@@ -17,6 +17,10 @@
 package org.jetbrains.kotlin.cli.common.arguments
 
 import kotlin.reflect.KClass
+import kotlin.reflect.KVisibility
 
 @Retention(AnnotationRetention.RUNTIME)
-annotation class GradleOption(val value: KClass<out DefaultValues> = DefaultValues::class)
+annotation class GradleOption(
+    val value: KClass<out DefaultValues> = DefaultValues::class,
+    val backingFieldVisibility: KVisibility = KVisibility.PRIVATE
+)

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JVMCompilerArguments.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.cli.common.arguments
 import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity
 import org.jetbrains.kotlin.cli.common.messages.MessageCollector
 import org.jetbrains.kotlin.config.*
+import kotlin.reflect.KVisibility
 
 class K2JVMCompilerArguments : CommonCompilerArguments() {
     companion object {
@@ -75,7 +76,10 @@ class K2JVMCompilerArguments : CommonCompilerArguments() {
     @Argument(value = "-module-name", valueDescription = "<name>", description = "Name of the generated .kotlin_module file")
     var moduleName: String? by NullableStringFreezableVar(null)
 
-    @GradleOption(DefaultValues.JvmTargetVersions::class)
+    @GradleOption(
+        value = DefaultValues.JvmTargetVersions::class,
+        backingFieldVisibility = KVisibility.INTERNAL
+    )
     @Argument(
         value = "-jvm-target",
         valueDescription = "<version>",