Effects: add diagnostic tests on contracts

- Make AbstractDiagnosticsTest dump function contracts
- Add diagnostics tests on parsing contracts
- Add diagnostics tests on smartcats in presence of functions with
contracts
- Add diagnostics tests on initialization and flow in presence of
in-place called lambdas

==========
Introduction of EffectSystem: 16/18

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/when/withSubject.kt

@@ -0,0 +1,35 @@
+// !LANGUAGE: +ReturnsEffect
+// !DIAGNOSTICS: -INVISIBLE_REFERENCE -INVISIBLE_MEMBER
+
+import kotlin.internal.contracts.*
+
+fun isString(x: Any?): Boolean {
+    contract {
+        returns(true) implies (x is String)
+    }
+    return x is String
+}
+
+fun exhaustive(x: Any?) {
+    when (isString(x)) {
+        true -> <!DEBUG_INFO_SMARTCAST!>x<!>.length
+        false -> x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+
+    when(!isString(x)) {
+        true -> x.<!UNRESOLVED_REFERENCE!>length<!>
+        false -> <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}
+
+fun smartcastInElse(x: Any?) {
+    when (isString(x)) {
+        false -> x.<!UNRESOLVED_REFERENCE!>length<!>
+        else -> <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+
+    when (!isString(x)) {
+        true -> x.<!UNRESOLVED_REFERENCE!>length<!>
+        else -> <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}