K2: Avoid losing diagnostics for synthetic calls

Some of the changed tests may duplicate other existing diagnostics,
but that should not be reason not to report them at all.

There might be another job to be done to avoid diagnostic duplications

compiler/frontend.common/src/org/jetbrains/kotlin/KtSourceElement.kt

@@ -251,6 +251,9 @@ sealed class KtFakeSourceElementKind(final override val shouldSkipErrorTypeRepor
 
     // for return type of value parameters in lambdas
     object ImplicitReturnTypeOfLambdaValueParameter : KtFakeSourceElementKind()
+
+    // Synthetic calls for if/when/try/etc.
+    object SyntheticCall : KtFakeSourceElementKind()
 }
 
 sealed class AbstractKtSourceElement {
@@ -503,4 +506,3 @@ inline fun LighterASTNode.toKtLightSourceElement(
     startOffset: Int = this.startOffset,
     endOffset: Int = this.endOffset
 ): KtLightSourceElement = KtLightSourceElement(this, startOffset, endOffset, tree, kind)
-