[FIR generator] Print accept method's body on new line

This is to unify the code formatting with IR classes

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/printer/element.kt

@@ -90,7 +90,10 @@ fun SmartPrinter.printElement(element: Element) {
             }
 
             override()
-            println("fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R = visitor.visit$name(this, data)")
+            println("fun <R, D> accept(visitor: FirVisitor<R, D>, data: D): R =")
+            withIndent {
+                println("visitor.visit${element.name}(this, data)")
+            }
 
             println()
             println("@Suppress(\"UNCHECKED_CAST\")")