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/controlStructures/specialConstructsAndPlatformTypes.kt

@@ -0,0 +1,39 @@
+// FILE: J.java
+import java.util.*;
+
+public class J {
+    public static String s = null;
+    public static Map<String, String> m = null;
+}
+
+// FILE: k.kt
+
+val testImplicitExclExcl1: String = J.s
+val testImplicitExclExcl2: String? = J.s
+
+val testImplicitExclExcl3: String = <!TYPE_MISMATCH!>J.m[""]<!>
+val testImplicitExclExcl4: String? = J.m[""]
+
+val testExclExcl1: String = J.s!!
+val testExclExcl2: String? = J.s!!
+
+val testExclExcl3: String = J.m[""]!!
+val testExclExcl4: String? = J.m[""]!!
+
+val testSafeCall1: String = <!TYPE_MISMATCH!>J.s?.let { it }<!>
+val testSafeCall2: String? = J.s?.let { it }
+
+val testSafeCall3: String = <!TYPE_MISMATCH!>J.m[""]?.let { it }<!>
+val testSafeCall4: String? = J.m[""]?.let { it.toString() }
+
+val testIf1: String = if (true) J.s else J.s
+val testIf2: String? = if (true) J.s else J.s
+
+val testIf3: String = if (true) <!TYPE_MISMATCH!>J.m[""]<!> else <!TYPE_MISMATCH!>J.m[""]<!>
+val testIf4: String? = if (true) J.m[""] else J.m[""]
+
+val testWhen1: String = when { else -> J.s }
+val testWhen2: String? = when { else -> J.s }
+
+val testWhen3: String = when { else -> <!TYPE_MISMATCH!>J.m[""]<!> }
+val testWhen4: String? = when { else -> J.m[""] }

compiler/testData/diagnostics/tests/controlStructures/specialConstructsAndPlatformTypes.txt

@@ -0,0 +1,33 @@
+package
+
+public val testExclExcl1: kotlin.String
+public val testExclExcl2: kotlin.String?
+public val testExclExcl3: kotlin.String
+public val testExclExcl4: kotlin.String?
+public val testIf1: kotlin.String
+public val testIf2: kotlin.String?
+public val testIf3: kotlin.String
+public val testIf4: kotlin.String?
+public val testImplicitExclExcl1: kotlin.String
+public val testImplicitExclExcl2: kotlin.String?
+public val testImplicitExclExcl3: kotlin.String
+public val testImplicitExclExcl4: kotlin.String?
+public val testSafeCall1: kotlin.String
+public val testSafeCall2: kotlin.String?
+public val testSafeCall3: kotlin.String
+public val testSafeCall4: kotlin.String?
+public val testWhen1: kotlin.String
+public val testWhen2: kotlin.String?
+public val testWhen3: kotlin.String
+public val testWhen4: kotlin.String?
+
+public open class J {
+    public constructor J()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public final var m: kotlin.collections.(Mutable)Map<kotlin.String!, kotlin.String!>!
+    public final var s: kotlin.String!
+}

compiler/testData/diagnostics/tests/controlStructures/specialConstructsWithNullableExpectedType.kt

@@ -0,0 +1,20 @@
+val ns: String? = null
+
+val testElvis1: String? = ns ?: ""
+val testElvis2: String = run { ns ?: "" }
+val testElvis3: String? = run { ns ?: "" }
+
+val testIf1: String? = if (true) "" else ""
+val testIf2: String? = run { if (true) "" else "" }
+val testIf3: String? = if (true) run { "" } else ""
+val testIf4: String? = run { run { if (true) "" else "" } }
+val testIf5: String? = run { if (true) run { "" } else "" }
+
+val testWhen1: String? = when { else -> "" }
+val testWhen2: String? = run { when { else -> "" } }
+val testWhen3: String? = when { else -> run { "" } }
+val testWhen4: String? = run { run { when { else -> "" } } }
+val testWhen5: String? = run { when { else -> run { "" } } }
+
+val testExcl1: String? = run { ns!! }
+val testExcl2: String? = run { run { ns!! } }

compiler/testData/diagnostics/tests/controlStructures/specialConstructsWithNullableExpectedType.txt

@@ -0,0 +1,18 @@
+package
+
+public val ns: kotlin.String? = null
+public val testElvis1: kotlin.String?
+public val testElvis2: kotlin.String
+public val testElvis3: kotlin.String?
+public val testExcl1: kotlin.String?
+public val testExcl2: kotlin.String?
+public val testIf1: kotlin.String?
+public val testIf2: kotlin.String?
+public val testIf3: kotlin.String?
+public val testIf4: kotlin.String?
+public val testIf5: kotlin.String?
+public val testWhen1: kotlin.String?
+public val testWhen2: kotlin.String?
+public val testWhen3: kotlin.String?
+public val testWhen4: kotlin.String?
+public val testWhen5: kotlin.String?