Move coroutine-related runtime parts to kotlin.coroutines.experimental package

#KT-15975 Fixed

idea/testData/decompiler/stubBuilder/Modifiers/Modifiers.kt

@@ -1,5 +1,5 @@
 package test
-import kotlin.coroutines.*
+import kotlin.coroutines.experimental.*
 
 data class Modifiers(val x: Int) {
     external fun extFun()

idea/testData/decompiler/stubBuilder/Modifiers/Modifiers.txt

@@ -139,8 +139,10 @@ PsiJetFileStubImpl[package=test]
               USER_TYPE
                 USER_TYPE
                   USER_TYPE
-                    REFERENCE_EXPRESSION[referencedName=kotlin]
-                  REFERENCE_EXPRESSION[referencedName=coroutines]
+                    USER_TYPE
+                      REFERENCE_EXPRESSION[referencedName=kotlin]
+                    REFERENCE_EXPRESSION[referencedName=coroutines]
+                  REFERENCE_EXPRESSION[referencedName=experimental]
                 REFERENCE_EXPRESSION[referencedName=Continuation]
                 TYPE_ARGUMENT_LIST
                   TYPE_PROJECTION[projectionKind=NONE]