docs: fix self-referential JSDoc for forEachContext param

[KangaZero]

Summary

The JSDoc description for the forEachContext parameter in forEachChildren is self-referential:

```js

• @param {*} forEachContext Context for forEachContext.
  ```

The description names the parameter in its own definition, which is meaningless. forEachContext is the execution context (this) passed to forEachFunc when it is called. The sibling mapChildren function (line 363) shows the correct pattern:

```js

• @param {*} context Context for mapFunction.
  ```

How did you test this change?

Documentation-only change to a JSDoc comment — no runtime behavior is affected, no tests needed. Verified by:

1. Comparing with the sibling mapChildren function's @param {*} context Context for mapFunction. description, which uses the same convention (naming the callback the context belongs to, not the parameter itself).
2. Confirming the parameter's purpose: forEachContext is passed as the this value in forEachFunc.apply(this, arguments) (line 424), so "Context for forEachFunc" is factually correct.

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[daltino]

This PR fixes a small but notable typo in the JSDoc for the forEachContext parameter by correctly referencing it as the context for forEachFunc. The change improves the documentation clarity, aligning with React's commitment to precise and helpful comments.