fix: role="searchbox" should assing "SearchField" trait on iOS (#39314)

Summary:
Experimenting with Accessibility Inspector on iOS I've discovered that while when assigning `accessibilityRole="searchbox"` to a text input results in "Traits" reporting "Search Field" trait. However, when using ARIA-compatible `role="search"` such trait is not assigned, and text input will have an empty trait.

Afaiu this is incorrect as using `role="search"` and `accessibilityRole="searchbox"` should equivalent effect.

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IOS FIXED - `role="searchbox"` now assigns "Search Field" accessibility trait to a view

Pull Request resolved: #39314

Test Plan: No UI changes, it affects only accessibility.

Reviewed By: NickGerleman

Differential Revision: D49014039

Pulled By: dmytrorykun

fbshipit-source-id: 5fb194e67fbf2ac339d9a746e3ce6aaed2d32558

packages/react-native/React/Views/RCTViewManager.m

@@ -92,7 +92,7 @@ @implementation RCTConvert (UIAccessibilityTraits)
       @"scrollbar" : @(UIAccessibilityTraitNone),
       @"scrollview" : @(UIAccessibilityTraitNone),
       @"search" : @(UIAccessibilityTraitSearchField),
-      @"searchbox" : @(UIAccessibilityTraitNone),
+      @"searchbox" : @(UIAccessibilityTraitSearchField),
       @"selected" : @(UIAccessibilityTraitSelected),
       @"separator" : @(UIAccessibilityTraitNone),
       @"slider" : @(UIAccessibilityTraitNone),