dillon1000/react

Add credentialless as a recognized boolean attribute for iframes (#36148)

## Summary

The `credentialless` attribute is a boolean HTML attribute for
`<iframe>` elements that loads the iframe in a new, ephemeral context
without access to the parent's credentials (cookies, client
certificates, etc.). This change adds it to all boolean attribute
switch/case lists in React DOM so it is properly handled as a boolean
(set when true, removed when false) rather than being treated as an
unknown string attribute.

Per the [Anonymous iframe spec
(WICG)](https://wicg.github.io/anonymous-iframe/):

> The credentialless attribute enables loading documents hosted by the
iframe with a new and ephemeral storage partition. It is a boolean
value. The default is false.

```
partial interface HTMLIFrameElement {
  attribute boolean credentialless; 
};
```

Changes:
- ReactDOMComponent.js: Added to both `setProp` and
`diffHydratedGenericElement`
- ReactFizzConfigDOM.js: Added to `pushAttribute` for server-side
rendering
- ReactDOMUnknownPropertyHook.js: Added to both validation switch/case
lists

## Test plan

- Added unit test in DOMPropertyOperations-test.js verifying
`credentialless={true}` sets the attribute to `''` and
`credentialless={false}` removes it
- All tests pass in source and www channels (590 tests each)
- Flow type checking passes (dom-node renderer)
- Prettier and lint pass