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/smartCastProvider/smartCastInfo/bothImplicitReceiversSmartCast.kt

@@ -0,0 +1,18 @@
+interface Foo {
+    fun Bar.foo()
+}
+
+interface Bar {}
+
+inline fun <T, R> myWith(argument: T, lambda: T.() -> R): R {
+    argument.lambda()
+}
+
+fun Any.action(other: Any) {
+    if (this is Foo) {
+        with(other) {
+            this as Bar
+            <expr>foo</expr>()
+        }
+    }
+}

analysis/analysis-api/testData/components/smartCastProvider/smartCastInfo/bothImplicitReceiversSmartCast.txt

@@ -0,0 +1,7 @@
+expression: foo
+isStable: null
+smartCastType: null
+receiver: DISPATCH
+    smartCastType: Foo
+receiver: EXTENSION
+    smartCastType: Bar