fix: iOS honor RCTI18nUtil RTL on New Architecture

[kashmiry]

Summary:

On the New Architecture (Fabric) on iOS, the slider follows the device language instead of the app's language.
So if the app is in (RTL) and forced with:

I18nManager.forceRTL(true)

but the device is in English (LTR), the slider appears flipped — the filled side and drag direction don't match the rest of the app's UI. Same problem in reverse: English app on an Arabic device.

This fix makes the slider follow the app's direction (I18nManager.forceRTL) regardless of what the device is set to.

• Android already works correctly, so no changes there.
• The old architecture (Paper) is unaffected.

issue.mov

fixed.mov

Test Plan:

Tested on the New Architecture (Fabric) on iOS with all four combinations of device locale × app forced direction. The slider's filled track grows from the value-minimum side as defined by the app's direction in every case:

Device locale	App forced direction	Expected filled-from-side	Result
LTR (en_US)	LTR	Left	✅
LTR (en_US)	RTL (forceRTL(true))	Right	✅
RTL (ar_SA)	LTR (forceRTL(false))	Left	✅
RTL (ar_SA)	RTL	Right	✅

Also verified:

• Dragging toward the maximum side increases the value, regardless of device locale.
• tapToSeek taps land at the correct value in all four combinations.
• The inverted prop still works on top of the new baseline direction.
• No regressions on Android.

Repro steps (before the fix):

1. Run on iOS with New Architecture enabled.
2. Ensure iOS project has a localized Info.plist example for Arabic (RTL language)
3. Set device language to English; in the app, call I18nManager.forceRTL(true) and restart.
4. Observe the slider's filled track is on the left (incorrect — should be on the right to match the app's RTL UI).
5. Apply this patch, rebuild, and observe the filled track is now on the right.

[BartoszKlonowski]

There can still be an issue with the original thumb with the RTL approach, but this is not related to that PR. We also still support inverted prop, which works fine on iOS platform in that case.
Still, I see the point of this PR and I see no stopping issues with it 👍
Thank you, @kashmiry for handling this :)

[BartoszKlonowski]

I don't see a way to approve the workflow for some reason, so let me reopen hoping to fix it...