Migrate UseExperimental->OptIn in project sources

libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt

@@ -444,7 +444,7 @@ private fun renderAnnotation(annotation: KmAnnotation): String =
             "$name = ${renderAnnotationArgument(argument)}"
         }
 
-@UseExperimental(ExperimentalUnsignedTypes::class)
+@OptIn(ExperimentalUnsignedTypes::class)
 private fun renderAnnotationArgument(arg: KmAnnotationArgument<*>): String =
     when (arg) {
         is KmAnnotationArgument.ByteValue -> arg.value.toString() + ".toByte()"

libraries/tools/kotlinp/testData/Contracts.kt

@@ -1,4 +1,4 @@
-@file:UseExperimental(ExperimentalContracts::class)
+@file:OptIn(ExperimentalContracts::class)
 
 import kotlin.contracts.InvocationKind
 import kotlin.contracts.contract