8312491: Update Classfile API snippets and examples

Reviewed-by: jlahoda

src/java.base/share/classes/jdk/internal/classfile/instruction/LocalVariable.java

@@ -80,6 +80,12 @@ public sealed interface LocalVariable extends PseudoInstruction
      */
     Label endScope();
 
+    /**
+     * Writes the local variable to the specified writer
+     *
+     * @param buf the writer
+     * @return true if the variable has been written
+     */
     boolean writeTo(BufWriter buf);
 
     /**