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/testData/diagnostics/tests/coroutines/suspendApplicability.kt

@@ -8,7 +8,7 @@ class Controller {
 
     }
 
-    inline <!INAPPLICABLE_MODIFIER!>suspend<!> fun inlineFun(x: Continuation<Int>) {
+    inline suspend fun inlineFun(x: Continuation<Int>) {
 
     }