refactor(iOS, FormSheet v5): Move detents resolving to dedicated class

[t0maboro]

Description

Move buildSheetDetents, consumeInitialDetentIdentifierForDetents, largestUndimmedDetentIdentifierForDetents, areDetentsValid, areDetentsStrictlyAscending to a dedicated file. All logic related to transforming JS payload to native detents should now go through this file.

Changes

• moved methods responsible for building detents and resolving identifiers based on JS payload was moved to a dedicated class

Before & after - visual documentation

N/A

Test plan

I went through all SFTs for FormSheet, especially related to largestUndimmedDetentIndex & initialDetentIndex.

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 extracts detent-related logic from RNSFormSheetHostComponentView into a new dedicated class RNSFormSheetDetentResolver. The refactor is behavior-preserving: building native detents from JS fractions, resolving the initial selected detent identifier, and resolving the largest-undimmed detent identifier are now static class methods on the new resolver. The _initialDetentApplied "consume-once" flag is now managed in the caller rather than inside the moved method.

Changes:

• Added RNSFormSheetDetentResolver header/implementation hosting buildSheetDetentsForFractions:, initialDetentIdentifierForDetents:atRequestedIndex:, and largestUndimmedDetentIdentifierForDetents:atIndex:, plus moved the kRNSFormSheetLastDetent / kRNSFormSheetAlwaysDimmed / kRNSFormSheetNeverDimmed sentinel constants into the header.
• Removed the equivalent private methods and constants from RNSFormSheetHostComponentView.mm; the host now delegates to the resolver and toggles _initialDetentApplied itself.
• areDetentsValid / areDetentsStrictlyAscending become file-scope C++ helpers (RNSAreDetentsValid / RNSAreDetentsStrictlyAscending) inside the new translation unit.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
ios/gamma/modals/form-sheet/RNSFormSheetDetentResolver.h	New header declaring the resolver class and sentinel index constants; uses #pragma once consistent with sibling headers and gates the C++ vector-based selector behind __cplusplus.
ios/gamma/modals/form-sheet/RNSFormSheetDetentResolver.mm	New implementation containing the moved detent-building and identifier-resolution logic, with the validity/ordering checks as static C++ helpers; whole @implementation is wrapped in #if !TARGET_OS_TV.
ios/gamma/modals/form-sheet/RNSFormSheetHostComponentView.mm	Removes moved methods and constants; updateConfiguration now calls the resolver and manages the one-shot _initialDetentApplied flag locally.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.