JVM_IR: make continuation detection more consistent

* unify various checks for whether a suspend function needs a
    continuation;

  * mark the continuation parameter with an origin (this also allows
    correctly computing the offset of the local in codegen -- see the
    new test);

  * when wrapping `suspend fun main`, use a suspend reference instead of
    a synthetic non-suspend lambda (required to correctly implement the
    previous point, as previously the continuation parameter was passed
    to main() itself correctly only because of very lenient checks in
    AddContinuationLowering).

compiler/testData/codegen/boxInline/suspend/nestedMethodWith2XParameter.kt

@@ -0,0 +1,22 @@
+// WITH_RUNTIME
+// WITH_COROUTINES
+// TARGET_BACKEND: JVM
+// FILE: a.kt
+
+inline suspend fun f(crossinline lambda: suspend (Double) -> Double): Double {
+    val obj = object {
+        suspend fun g(x: Double): Double = lambda(x)
+    }
+    return obj.g(1.0)
+}
+
+// FILE: b.kt
+import helpers.*
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+fun box(): String {
+    var result: Double = 0.0
+    suspend { result = f { it } }.startCoroutine(EmptyContinuation)
+    return if (result == 1.0) "OK" else "fail: $result"
+}