Minor DOM FragmentInstance refactors

[everettbu]

Mirror of facebook/react#35641
Original author: jackpope

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Handles TODOs, small follow up refactors

[greptile-apps]

Greptile Overview

Greptile Summary

This PR does small cleanup/refactor work in ReactFiberConfigDOM.js around FragmentInstance DOM APIs:

• indexOfEventListener now early-returns on empty arrays and caches normalized listener options to avoid recomputing during the loop.
• FragmentInstance.blur() now computes activeElement once, bails out early if it’s not within the fragment’s parent host instance, and passes activeElement into the traversal callback.
• Minor variable renames in compareDocumentPosition (element → node) for clarity.

I did not find any merge-blocking issues introduced by these changes.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk.
• Changes are localized refactors that preserve existing behavior (option normalization caching, early exit in blur traversal, and variable renames) and do not affect external interfaces.
• No files require special attention

Important Files Changed

Filename	Overview
packages/react-dom-bindings/src/client/ReactFiberConfigDOM.js	Small refactors in FragmentInstance helpers: cache normalized event listener options, optimize blur() traversal by passing activeElement, and rename compareDocumentPosition locals; no functional issues found.

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[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.