Add ExperimentalContracts opt-in

Author: igoriakovlev

src/wasmJsMain/kotlin/main.kt

@@ -1,5 +1,6 @@
 import kotlinx.browser.document
 
+@OptIn(kotlin.contracts.ExperimentalContracts::class)
 fun main() {
   document.body?.addTimeZoneWidget()
 }

src/wasmJsMain/kotlin/timeZoneWidget.kt

@@ -5,6 +5,7 @@ import kotlinx.dom.appendText
 import org.w3c.dom.Element
 import org.w3c.dom.HTMLInputElement
 
+@kotlin.contracts.ExperimentalContracts
 fun Element.addTimeZoneWidget() {
     appendElement("div") {
         appendText("Time in ")

src/wasmJsTest/kotlin/Test.kt

@@ -1,10 +1,12 @@
 import kotlinx.browser.document
 import org.w3c.dom.HTMLInputElement
 import org.w3c.dom.get
+import kotlin.contracts.ExperimentalContracts
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
 class BrowserTest {
+    @OptIn(ExperimentalContracts::class)
     @Test
     fun mainTest() {
         val mockContainer = document.createElement("div")