Allow calling some pieces of the experimental coroutine API

- Calling suspend functions is allowed
- Presence of suspend function type still makes declaration
unusable unless it belongs to a value parameter as a top-level type
containing less then three parameters

Still, warning should be emitted because they will become unsupported in 1.4

 #KT-25683 In Progress

compiler/testData/compileKotlinAgainstCustomBinaries/experimentalCoroutineCallFromRelease/library/experimental.kt

@@ -1,27 +1,14 @@
-suspend fun dummy() {}
-
-class C {
-    suspend fun dummy() = "OK"
-}
-
-class WithNested {
-    class Nested {
-        suspend fun dummy() = "OK"
-    }
-}
-
-class WithInner {
-    inner class Inner {
-        suspend fun dummy() = "OK"
-    }
-}
-
 val c: suspend () -> Unit = {}
 
 class WithTypeParameter<T: suspend() -> Unit> {}
 
 fun returnsSuspend() : suspend() -> Unit = {}
 
-fun builder(c: suspend () -> Unit) {}
+fun <T: suspend () -> Unit> withTypeParameter() = {}
 
-fun <T: suspend () -> Unit> withTypeParameter() = {}
+fun suspendFunctionNested(x: List<suspend () -> Unit>) {}
+fun suspendFunctionNestedInFunctionType(x: (suspend () -> Unit) -> Unit) {}
+
+fun suspendFunctionType3(x: suspend (Int, Int, Int) -> Unit) {}
+
+fun suspendVarargs(vararg x: suspend () -> Unit) {}