Migrate UseExperimental->OptIn in project sources

libraries/stdlib/test/time/DurationTest.kt

@@ -3,7 +3,7 @@
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
-@file:UseExperimental(ExperimentalTime::class)
+@file:OptIn(ExperimentalTime::class)
 package test.time
 
 import test.numbers.assertAlmostEquals
@@ -398,4 +398,4 @@ class DurationTest {
         test(Duration.INFINITE, "Infinity")
     }
 
-}
+}