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/compositions.kt

@@ -0,0 +1,69 @@
+// !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 testEqualsWithConstant(x: Any?) {
+    if (isString(x) == true) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun testNotEqualsWithConstant(x: Any?) {
+    if (isString(x) != true) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}
+
+fun unknownFunction(): Any? = 42
+
+fun testEqualsWithUnknown(x: Any?) {
+    if (isString(x) == unknownFunction()) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testNotEqualsWithUnknown(x: Any?) {
+    if (isString(x) != unknownFunction()) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testEqualsWithVariable(x: Any?, b: Boolean) {
+    if (isString(x) == b) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun testNotEqualsWithVariable(x: Any?, b: Boolean) {
+    if (isString(x) != b) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}