Rename UseExperimental->OptIn, Experimental->RequiresOptIn in Gradle plugin

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/NewMultiplatformIT.kt

@@ -542,8 +542,8 @@ class NewMultiplatformIT : BaseGradleIT() {
                 assertTasksExecuted(":$it")
                 assertContains(
                     "-language-version 1.3", "-api-version 1.3", "-XXLanguage:+InlineClasses",
-                    " -progressive", "-Xuse-experimental=kotlin.ExperimentalUnsignedTypes",
-                    "-Xuse-experimental=kotlin.contracts.ExperimentalContracts"
+                    " -progressive", "-Xopt-in=kotlin.ExperimentalUnsignedTypes",
+                    "-Xopt-in=kotlin.contracts.ExperimentalContracts"
                 )
             }
         }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/DefaultLanguageSettingsBuilder.kt

@@ -103,7 +103,7 @@ internal fun applyLanguageSettingsToKotlinTask(
     }
 
     languageSettingsBuilder.experimentalAnnotationsInUse.forEach { annotationName ->
-        freeCompilerArgs += "-Xuse-experimental=$annotationName"
+        freeCompilerArgs += "-Xopt-in=$annotationName"
     }
 }
 

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/native/tasks/KotlinNativeTasks.kt

@@ -354,7 +354,7 @@ open class KotlinNativeCompile : AbstractKotlinNativeCompile<KotlinCommonOptions
             add("-XXLanguage:+$featureName")
         }
         experimentalAnnotationsInUse.forEach { annotationName ->
-            add("-Xuse-experimental=$annotationName")
+            add("-Xopt-in=$annotationName")
         }
     }
 
@@ -545,7 +545,7 @@ open class KotlinNativeLink : AbstractKotlinNativeCompile<KotlinCommonToolOption
                     add("-XXLanguage:+$featureName")
                 }
                 it.experimentalAnnotationsInUse.forEach { annotationName ->
-                    add("-Xuse-experimental=$annotationName")
+                    add("-Xopt-in=$annotationName")
                 }
             }
         }