[lexical][@lexical/selection] Feature: add a generic classes property to all nodes for easier customization

packages/lexical/src/LexicalNode.ts

@@ -208,7 +208,7 @@ export class LexicalNode {
    */
   getClasses(): ReadonlyClasses {
     const self = this.getLatest();
-    return {...self.__classes};
+    return self.__classes || {};
   }
 
   /**
@@ -233,9 +233,7 @@ export class LexicalNode {
     } else {
       classes[key] = value;
     }
-    if (Object.keys(classes).length > 0) {
-      self.__classes = classes;
-    }
+    self.__classes = classes;
   }
 
   // Flow doesn't support abstract classes unfortunately, so we can't _force_
@@ -325,6 +323,7 @@ export class LexicalNode {
     this.__parent = prevNode.__parent;
     this.__next = prevNode.__next;
     this.__prev = prevNode.__prev;
+    this.__classes = {...prevNode.__classes};
   }
 
   // eslint-disable-next-line @typescript-eslint/no-explicit-any

packages/lexical/src/LexicalUtils.ts

@@ -1436,9 +1436,6 @@ export function $isRootOrShadowRoot(
  */
 export function $copyNode<T extends LexicalNode>(node: T): T {
   const copy = node.constructor.clone(node) as T;
-  if (node.__classes) {
-    copy.__classes = {...node.__classes};
-  }
   $setNodeKey(copy, null);
   return copy;
 }
@@ -1844,9 +1841,6 @@ export function getCachedTypeToNodeMap(
 export function $cloneWithProperties<T extends LexicalNode>(latestNode: T): T {
   const constructor = latestNode.constructor;
   const mutableNode = constructor.clone(latestNode) as T;
-  if (latestNode.__classes) {
-    mutableNode.__classes = {...latestNode.__classes};
-  }
   mutableNode.afterCloneFrom(latestNode);
   if (__DEV__) {
     invariant(