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/throwsEffect.kt

@@ -0,0 +1,65 @@
+// !LANGUAGE: +ReturnsEffect
+// !DIAGNOSTICS: -INVISIBLE_REFERENCE -INVISIBLE_MEMBER
+
+import kotlin.internal.contracts.*
+
+fun myAssert(condition: Boolean) {
+    contract {
+        returns() implies (condition)
+    }
+    if (!condition) throw kotlin.IllegalArgumentException("Assertion failed")
+}
+
+fun testAssertSmartcast(x: Any?) {
+    myAssert(x is String)
+    <!DEBUG_INFO_SMARTCAST!>x<!>.length
+}
+
+fun testInvertedAssert(x: Any?) {
+    myAssert(x !is String)
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testSpilling(x: Any?) {
+    if (x != null) {
+        myAssert(x is String)
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testAssertInIf(x: Any?) {
+    if (myAssert(x is String) == Unit) {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    else {
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+}
+
+fun testTryCatch(x: Any?) {
+    try {
+        myAssert(x is String)
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    } catch (e: kotlin.IllegalArgumentException) {
+
+    }
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testUncertainFlow(x: Any?) {
+    repeat(x.toString().length) {
+        myAssert(x is String)
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    }
+    x.<!UNRESOLVED_REFERENCE!>length<!>
+}
+
+fun testAtLeastOnceFlow(x: Any?) {
+    do {
+        myAssert(x is String)
+        <!DEBUG_INFO_SMARTCAST!>x<!>.length
+    } while (x != null)
+
+    <!DEBUG_INFO_SMARTCAST!>x<!>.length
+}