K2 Tests: Add rendering of FirSmartCastExpression in html dump

Previously it was just skipped

compiler/fir/dump/resources/org/jetbrains/kotlin/fir/dump/colors.dark.css

@@ -102,4 +102,8 @@ body.dark {
 .dark .diagnostic-hover {
     background-color: #3a3a3a;
     color: #dfdfdf;
+}
+
+.dark .smart-cast {
+    background-color: #223C23;
 }

compiler/fir/dump/resources/org/jetbrains/kotlin/fir/dump/colors.white.css

@@ -92,4 +92,8 @@
 .white .diagnostic-hover {
     background-color: #eaeaea;
     color: #000;
+}
+
+.white .smart-cast {
+    background-color: #DBFFDB;
 }

compiler/fir/dump/src/org/jetbrains/kotlin/fir/dump/HtmlFirDump.kt

@@ -1590,6 +1590,7 @@ class HtmlFirDump internal constructor(private var linkResolver: FirLinkResolver
                 is FirCheckedSafeCallSubject -> {
                     +"\$subj\$"
                 }
+                is FirSmartCastExpression -> generate(expression)
                 else -> inlineUnsupported(expression)
             }
         }
@@ -1601,6 +1602,12 @@ class HtmlFirDump internal constructor(private var linkResolver: FirLinkResolver
         generate(comparisonExpression.right)
     }
 
+    private fun FlowContent.generate(smartCastExpression: FirSmartCastExpression) {
+        span(classes = "smart-cast") {
+            generate(smartCastExpression.originalExpression)
+        }
+    }
+
     private fun FlowContent.generate(safeCallExpression: FirSafeCallExpression) {
         generate(safeCallExpression.receiver)