[introspection] Evaluate using UITextChecker.RequestGrammarChecking in ApiTypoTest

## Summary
Investigate whether `UITextChecker.RequestGrammarChecking` would improve the introspection typo test.

## Context
In PR #25889 (`[UIKit] Bind new Xcode 27 (iOS 27) UIKit APIs`), a review question came up about whether the new `UITextChecker.RequestGrammarChecking` API could provide any benefit to `tests/introspection/ApiTypoTest.cs`.

The current typo test collects words from public API names and checks each word individually with the spell checker:
- macOS: `SpellChecker.CheckSpelling`
- UIKit platforms: `UITextChecker.RangeOfMisspelledWordInString`

## Task
Evaluate whether `UITextChecker.RequestGrammarChecking` would improve typo detection in `ApiTypoTest`, and if so, how to integrate it without regressing the current test behavior.

## References
- `src/uikit.cs:24562-24569`
- `tests/introspection/ApiTypoTest.cs:937-969`
- PR #25889 comment thread: https://github.com/dotnet/macios/pull/25889#discussion_r3505015074

Read tests/introspection/ApiTypoTest.cs:937-969 and src/uikit.cs:24562-24569, then review the PR #25889 comment thread for the motivation. Compare RequestGrammarChecking with the existing macOS and UIKit spell-check paths, and determine whether it improves detection without changing current behavior; document the conclusion and integration approach.

Written by the indexing model from the issue text.