Moved tapAndAssertElementAppears to AssetUITestCase

[JunDangIntuit]

tapAndAssertElementAppears solves a generic UI-test race (tap before async SwiftUI/JS binding wires up) — not something specific to managed-player tests. Keeping it private forces other UI tests to copy or reinvent it. Moving it to the shared AssetUITestCase (next to waitFor/waitAndTap/tap) gives every UI test one canonical, public helper with no extra imports.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (23a98a4) to head (6d92826).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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