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/multieffect/implicitIff.kt

@@ -0,0 +1,86 @@
+// !LANGUAGE: +ReturnsEffect
+// !DIAGNOSTICS: -INVISIBLE_REFERENCE -INVISIBLE_MEMBER
+
+import kotlin.internal.contracts.*
+
+fun onlyTrue(b: Boolean): Boolean {
+    contract {
+        returns(true) implies (b)
+    }
+    return b
+}
+
+fun onlyFalse(b: Boolean): Boolean {
+    contract {
+        returns(false) implies (!b)
+    }
+    return b
+}
+
+fun trueAndFalse(b: Boolean): Boolean {
+    contract {
+        returns(true) implies (b)
+        returns(false) implies (!b)
+    }
+    return b
+}
+
+
+
+// ==== actual tests ====
+
+fun useOnlyTrueInTrueBranch(x: Any?) {
+    if (onlyTrue(x is String)) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun useOnlyTrueInFalseBranch(x: Any?) {
+    if (onlyTrue(x !is String)) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        // No smartcast here, we don't know that condition is false here
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun useOnlyFalseInTrueBranch(x: Any?) {
+    if (onlyFalse(x is String)) {
+        // No smartcast here, we don't know that condition is true here
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun useOnlyFalseInFalseBranch(x: Any?) {
+    if (onlyFalse(x !is String)) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}
+
+fun useTrueAndFalseInTrueBranch(x: Any?) {
+    if (trueAndFalse(x is String)) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    else {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+}
+
+fun useTrueAndFalseInFalseBranch(x: Any?) {
+    if (trueAndFalse(x !is String)) {
+        x.<!UNRESOLVED_REFERENCE!>length<!>
+    }
+    else {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}