Support inline suspend functions

A lot of additional work was required to support them:
- Suspension points are being identified by two markers
  instead of one pointing to suspend function call
- Approach with replacing return type of suspend function does not work anymore.
  So we decode suspension return type as an argument for begin marker
- It became necessary to perform variables liveness analysis
  (see comment in org.jetbrains.kotlin.codegen.coroutines.CoroutineTransformerMethodVisitor.spillVariables)

compiler/resolution/src/org/jetbrains/kotlin/resolve/coroutine/coroutineUtil.kt

@@ -23,12 +23,13 @@ import org.jetbrains.kotlin.resolve.scopes.receivers.ExtensionReceiver
 import org.jetbrains.kotlin.types.KotlinType
 
 val SUSPENSION_POINT_KEY: FunctionDescriptor.UserDataKey<Boolean> = object : FunctionDescriptor.UserDataKey<Boolean> {}
+val REPLACED_SUSPENSION_POINT_KEY: FunctionDescriptor.UserDataKey<Boolean> = object : FunctionDescriptor.UserDataKey<Boolean> {}
 
 // Returns suspension function as it's visible within coroutines:
 // E.g. `fun <V> await(f: CompletableFuture<V>): V` instead of `fun <V> await(f: CompletableFuture<V>, machine: Continuation<V>): Unit`
 fun SimpleFunctionDescriptor.createCoroutineSuspensionFunctionView(): SimpleFunctionDescriptor? {
     if (!isSuspend) return null
-    val returnType = valueParameters.lastOrNull()?.returnType?.arguments?.getOrNull(0)?.type ?: return null
+    val returnType = getSuspensionPointReturnType() ?: return null
 
     val newOriginal =
             if (original !== this)
@@ -45,4 +46,6 @@ fun SimpleFunctionDescriptor.createCoroutineSuspensionFunctionView(): SimpleFunc
     }.build()!!
 }
 
+fun SimpleFunctionDescriptor.getSuspensionPointReturnType(): KotlinType? = valueParameters.lastOrNull()?.returnType?.arguments?.getOrNull(0)?.type
+
 class CoroutineReceiverValue(callableDescriptor: CallableDescriptor, receiverType: KotlinType) : ExtensionReceiver(callableDescriptor, receiverType)