fix: add 'tabbar' to role type for accessibility

[hayleyyryan]

Summary:

The tabbar role was removed from AccessibilityRole in 2018 (commit f39d092) as it was only available on iOS 10+. It was later added back to AccessibilityRole once the minimum iOS version increased.

However, when the separate Role type was introduced in 2022 for the role prop, tabbar was not included despite being present in AccessibilityRole. This inconsistency causes TypeScript compilation errors when trying to use role="tabbar" on components, even though it's a valid and working accessibility role that exists in AccessibilityRole.

This PR adds tabbar to the Role type definition to maintain consistency between AccessibilityRole and Role, allowing developers to use this role without TypeScript errors and for accurate announcements for screen reader users.

Changelog:

Test Plan:

Before this change, the following TypeScript code would fail compilation:

<View role="tabbar">
  {/* ... */}
</View>

After this change, the code compiles successfully. The tabbar role also already exists in AccessibilityRole (line 213 of ViewAccessibility.d.ts) and works correctly at runtime on all currently supported iOS versions.

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[react-native-bot]

This PR is stale because it has been open for 180 days with no activity. It will be closed in 7 days unless you comment on it or remove the "Stale" label.

[popsiclelmlm]

This looks directionally right, but I think it needs a couple more files before it can land cleanly.

role is typed in more than the hand-written ViewAccessibility.d.ts file:

• packages/react-native/Libraries/Components/View/ViewAccessibility.js has the Flow Role union for the JS source, and it currently still has tab -> table without tabbar.
• packages/react-native/ReactNativeApi.d.ts is the generated public API snapshot, and its Role union also still lacks "tabbar".

So this PR should update the Flow source type and run yarn build-types / yarn build-types --validate so the API snapshot is updated too. Otherwise TypeScript users may be fixed in one declaration file, but the checked public API surface will still be out of sync.

Also, the changelog entry appears to be inside the template HTML comment. It should be outside the comment block, e.g. [IOS] [FIXED] - Add tabbar to the role type for accessibility.

[cortinico]

https://github.com/hayleyyryan/react-native/blob/a1e534a6042f4128b10059891d05c7b0953e60c0/packages/react-native/Libraries/Components/View/ViewAccessibility.d.ts#L214

No longer needed