feat(iOS, FormSheet v5): Emit onDismiss event when dismissed from JS

[t0maboro]

Description

Adding onDismiss event, which will be fired when the sheet is dismissed programmatically from JS via toggling isOpen prop to false.

Closes: https://github.com/software-mansion/react-native-screens-labs/issues/1268

Changes

• updated spec
• updated public API
• added native implementation

Before & after - visual documentation

iOS 26
ios25.mov

Test plan

Added dedicated SFT

Checklist

• Included code example that can be used to test this change.
• For visual changes, included screenshots / GIFs / recordings documenting the change.
• For API changes, updated relevant public types.
• Ensured that CI passes

[Copilot]

Pull request overview

This PR adds a new onDismiss callback to the experimental FormSheet API to notify JS when the sheet has been dismissed programmatically (by toggling isOpen to false). This helps consumers distinguish JS-driven dismissal from user-driven native gesture dismissal (onNativeDismiss).

Changes:

• Extended the Fabric/codegen spec and public TypeScript types to include onDismiss.
• Implemented iOS native emission of onDismiss when the sheet is dismissed via the presentation manager.
• Added a dedicated iOS single-feature-test scenario to validate onDismiss vs onNativeDismiss.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/fabric/gamma/modals/form-sheet/FormSheetHostNativeComponent.ts	Adds onDismiss to the codegen native component event props.
src/components/gamma/modals/form-sheet/FormSheet.types.ts	Exposes onDismiss in the public FormSheetProps API with docs.
ios/gamma/modals/form-sheet/RNSFormSheetPresentationManager.mm	Triggers a delegate callback after programmatic dismissal completes.
ios/gamma/modals/form-sheet/RNSFormSheetHostEventEmitter.mm	Implements native emission for the new onDismiss event.
ios/gamma/modals/form-sheet/RNSFormSheetHostEventEmitter.h	Declares the new emitOnDismiss method.
ios/gamma/modals/form-sheet/RNSFormSheetHostComponentView.mm	Implements sheetControllerDidDismiss and forwards to the event emitter.
ios/gamma/modals/form-sheet/RNSFormSheetContentController.h	Extends the delegate protocol with sheetControllerDidDismiss.
apps/src/tests/single-feature-tests/form-sheet/test-form-sheet-dismiss-events-ios/scenario.md	Adds a manual test scenario covering both dismiss event types.
apps/src/tests/single-feature-tests/form-sheet/test-form-sheet-dismiss-events-ios/scenario-description.ts	Registers metadata for the new SFT scenario.
apps/src/tests/single-feature-tests/form-sheet/test-form-sheet-dismiss-events-ios/index.tsx	Implements the test screen UI and logging for dismiss events.
apps/src/tests/single-feature-tests/form-sheet/index.ts	Adds the new dismiss-events scenario to the FormSheet scenario group.

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[LKuchno]

Good idea to put an event logs area on the screen! :)

[kligarski]

LGTM