Add deprecation warning for findDOMNode

This is removed in version 19. We already warned inside of Strict Mode
but this adds the warning everywhere.

packages/react-dom/src/client/ReactDOMLegacy.js

@@ -238,10 +238,22 @@ function legacyRenderSubtreeIntoContainer(
  return getPublicRootInstance(root);
 }
 
+let didWarnAboutFindDOMNode = false;
+
 export function findDOMNode(
  componentOrElement: Element | ?React$Component<any, any>,
 ): null | Element | Text {
  if (__DEV__) {
+ if (!didWarnAboutFindDOMNode) {
+ didWarnAboutFindDOMNode = true;
+ console.error(
+ 'findDOMNode is deprecated and will be removed in the next major ' +
+ 'release. Instead, add a ref directly to the element you want ' +
+ 'to reference. Learn more about using refs safely here: ' +
+ 'https://reactjs.org/link/strict-mode-find-node',
+ );
+ }
+
  const owner = (ReactCurrentOwner.current: any);
  if (owner !== null && owner.stateNode !== null) {
  const warnedAboutRefsInRender = owner.stateNode._warnedAboutRefsInRender;

scripts/jest/shouldIgnoreConsoleError.js

@@ -31,7 +31,8 @@ module.exports = function shouldIgnoreConsoleError(format, args) {
  'uses the legacy childContextTypes API which is no longer supported and will be removed'
  ) !== -1 ||
  format.indexOf('ReactDOMTestUtils is deprecated') !== -1 ||
- format.indexOf('`ReactDOMTestUtils.act` is deprecated') !== -1
+ format.indexOf('`ReactDOMTestUtils.act` is deprecated') !== -1 ||
+ format.indexOf('findDOMNode is deprecated and will be removed') !== -1
  ) {
  // This is a backported warning. In `main`, there's a different warning
  // (and it's fully tested). Not going to bother upgrading all the tests