Support val initialization in non-inline function with EXACTLY_ONCE effect

by generating a box for the value.
 #KT-26126 Fixed

compiler/testData/codegen/box/contracts/exactlyOnceNotInline.kt

@@ -0,0 +1,21 @@
+// !LANGUAGE: +AllowContractsForCustomFunctions +UseCallsInPlaceEffect +ReadDeserializedContracts
+// !USE_EXPERIMENTAL: kotlin.contracts.ExperimentalContracts
+// IGNORE_BACKEND: JVM_IR, NATIVE, JS_IR
+
+import kotlin.contracts.*
+
+@Suppress("INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
+public fun myrun(block: () -> Unit) {
+    contract {
+        callsInPlace(block, InvocationKind.EXACTLY_ONCE)
+    }
+    block()
+}
+
+fun box(): String {
+    val x: Long
+    myrun {
+        x = 1L
+    }
+    return if (x != 1L) "FAIL" else "OK"
+}