[IR][K/N] Extracted explicit var spilling phase from coroutines lowering

Not only does it give some flexibility but also it could be turned off
in the future (by providing trivial replacement) as a workaround

 #KT-65153

kotlin-native/runtime/src/main/kotlin/kotlin/native/internal/Coroutines.kt

@@ -25,3 +25,12 @@ internal inline suspend fun getCoroutineContext(): CoroutineContext =
 @TypedIntrinsic(IntrinsicType.RETURN_IF_SUSPENDED)
 @PublishedApi
 internal external suspend fun <T> returnIfSuspended(@Suppress("UNUSED_PARAMETER") argument: Any?): T
+
+@TypedIntrinsic(IntrinsicType.SAVE_COROUTINE_STATE)
+@PublishedApi
+internal external fun saveCoroutineState()
+
+@TypedIntrinsic(IntrinsicType.RESTORE_COROUTINE_STATE)
+@PublishedApi
+internal external fun restoreCoroutineState()
+

kotlin-native/runtime/src/main/kotlin/kotlin/native/internal/IntrinsicType.kt

@@ -64,6 +64,8 @@ internal class IntrinsicType {
         // Coroutines
         const val GET_CONTINUATION              = "GET_CONTINUATION"
         const val RETURN_IF_SUSPENDED           = "RETURN_IF_SUSPENDED"
+        const val SAVE_COROUTINE_STATE          = "SAVE_COROUTINE_STATE"
+        const val RESTORE_COROUTINE_STATE       = "RESTORE_COROUTINE_STATE"
 
         // Interop
         const val INTEROP_READ_PRIMITIVE        = "INTEROP_READ_PRIMITIVE"