Use OPT_IN instead of EXPERIMENTAL in diagnostic names

kotlin-native/backend.native/tests/codegen/mpp/mpp_optional_expectation.kt

@@ -1,4 +1,4 @@
-@file:Suppress("EXPERIMENTAL_API_USAGE_ERROR")
+@file:Suppress("OPT_IN_USAGE_ERROR")
 
 import kotlin.js.*
 

kotlin-native/backend.native/tests/interop/cpp/skia.kt

@@ -1,4 +1,4 @@
-@file:Suppress("EXPERIMENTAL_API_USAGE_ERROR")
+@file:Suppress("OPT_IN_USAGE_ERROR")
 
 import kotlinx.cinterop.*
 import kotlin.test.*

kotlin-native/backend.native/tests/interop/cpp/skiaSignature.kt

@@ -1,4 +1,4 @@
-@file:Suppress("EXPERIMENTAL_API_USAGE_ERROR")
+@file:Suppress("OPT_IN_USAGE_ERROR")
 
 import kotlinx.cinterop.*
 import kotlin.test.*

kotlin-native/tools/kotlin-native-gradle-plugin/src/test/groovy/org/jetbrains/kotlin/gradle/plugin/test/MultiplatformSpecification.groovy

@@ -87,7 +87,7 @@ class MultiplatformSpecification extends BaseKonanSpecification {
                     ["src", "main", "kotlin"],
                     "common.kt",
                     """\
-                        @file:Suppress("EXPERIMENTAL_API_USAGE_ERROR")
+                        @file:Suppress("OPT_IN_USAGE_ERROR")
                         @OptionalExpectation
                         expect annotation class Optional()