FIR. Refactor smart-cast representation in FIR tree

Make smart-casts non-transparent expression without delegation
to underlying FirQualifiedAccessExpression, as children delegation in
fir tree has unclear semantics
Remove two different kinds of tree nodes for smart-casts

analysis/analysis-api/testData/components/callResolver/resolveCall/whenSelectorSmartCast.txt

@@ -0,0 +1,14 @@
+KtSuccessCallInfo:
+  call = KtSimpleVariableAccessCall:
+    partiallyAppliedSymbol = KtPartiallyAppliedSymbol:
+      dispatchReceiver = null
+      extensionReceiver = null
+      signature = KtVariableLikeSignature:
+        name = obj
+        receiverType = null
+        returnType = kotlin.Any
+        symbol = obj: kotlin.Any
+        callableIdIfNonLocal = null
+    simpleAccess = Read:
+
+    typeArgumentsMapping = {}