Fix type inference issues for 'if' and 'when'.

Use 'expectedType' (when present) as an explicit type argument for a special construct call.
Unfortunately, this approach can't be used for elvis due to other elvis-related inference hacks.
Fixes KT-10807, KT-10811.
This also affects KT-6189: now we can infer proper type for 'if'.

If type inference for special call failed, and we found no type errors in sub-expressions,
report TYPE_INFERENCE_FAILED_ON_SPECIAL_CONSTRUCT error.
This (and the hack above) fixes KT-10809: code no longer compiles.

compiler/testData/diagnostics/tests/when/kt10811.kt

@@ -0,0 +1,24 @@
+interface Maybe<T>
+class Some<T>(val value: T) : Maybe<T>
+class None<T> : Maybe<T>
+
+fun <T> none() : None<T> = TODO()
+
+fun test1() : Maybe<String?> = if (true) none() else Some("")
+
+fun test2() : Maybe<String?> = when {
+    true -> none()
+    else -> Some("")
+}
+
+fun test3() : Maybe<String?> = when {
+    true -> none()
+    else -> Some<String?>("")
+}
+
+fun test4() : Maybe<String?> {
+    when ("") {
+        "a" -> return none()
+        else -> return Some<String?>("")
+    }
+}