fix: re-run transformer on transformerId prop change

[janicduplessis]

Description

When a consumer swaps the transformer prop on TransformerTextInput (e.g., a currency picker switching between USD/EUR/JPY instances), the native decorator only registered the new transformer in the registry — it did not re-run it on the existing displayed text. The user would see the old formatting until they typed a keystroke, at which point the new transformer would finally run. The example app worked around this with a useEffect([currency]) that called inputRef.current.update({ transform: true }) after every picker change.

Solution

iOS and Android both detect the transformerId change at the same place they already update the registry lookup, and additionally re-run the new transformer on the current text + selection when the change happens after mount. If the resulting value or selection differs, they apply it (and on iOS, notify the base text-input delegate so React's onChangeText fires once).

The initial prop set is excluded by checking that the previous transformerId was non-zero (the default before the first React-driven set) and that the backing text-input view is attached. The JS-side transformedDefaultValue continues to own the very first render.

The example app drops its useEffect workaround — switching the currency picker reformats the displayed amount on its own now.

Test plan

• Pod install + rebuild iOS, gradle rebuild Android (native code changed).
• In the example app, open the Currency card, type a few digits (e.g., 1234567 → \$12,345.67).
• Switch the picker to EUR — expect the displayed value to immediately reformat to 12.345,67 €.
• Switch to JPY — expect ￥1,234,567 (no decimals, all whole units).
• Switch back to USD — expect \$12,345.67 again.
• Confirm the keyboard cursor lands right after the last digit in each currency, and that subsequent typing still works as expected.