[FIR] Add opt-in annotation which prevents from using symbol.fir

compiler/visualizer/render-fir/build.gradle.kts

@@ -14,3 +14,9 @@ sourceSets {
     "main" { projectDefault() }
     "test" { }
 }
+
+tasks.withType<org.jetbrains.kotlin.gradle.dsl.KotlinCompile<*>> {
+    kotlinOptions {
+        freeCompilerArgs += "-Xopt-in=org.jetbrains.kotlin.fir.symbols.SymbolInternals"
+    }
+}