Use ValueOption to look up a reference's definition item

[xperiandri]

Description

FSharpFindUsagesService.onSymbolFound looks up which definition item a reference belongs to with Array.tryFind and Option. This repo's convention (FSharp.instructions.md) is voption in new and touched code; Common/Extensions.fs already has Array.tryFindV for this exact case.

definitionItems
|> Array.tryFindV (snd >> (=) doc.Project.FilePath)
|> ValueOption.map (fun (definitionItem, _) -> definitionItem)
|> ValueOption.defaultValue externalDefinitionItem

Split out of #20533's review, where this line sat unchanged in the diff context.

Checklist

• Test cases added: none, behavior is unchanged.
• Performance benchmarks added in case of performance changes
• Release notes entry updated: not applicable, no user-visible change.

🤖 Generated with Claude Code

[github-actions]

❗ Release notes required

You can open this PR in browser to add release notes: open in github.dev

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md

[github-actions]

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: Changes IDE Find Usages execution.

Generated by PR Tooling Safety Check · gpt56 964.8K · ◷

[T-Gro]

🤖 🕵️ LGTM

[T-Gro]

🤖🕵️ Please shorten the description using this guidance. Focus on the problem and why the change is needed, in simplified technical English. Leave the implementation inventory to the Files tab and retain necessary caveats.

[xperiandri]

This is already short enough, no?

[T-Gro]

@xperiandri :

Apologies, my wording wasn't clear - in this case it's not shortness.
Its about not re-narrating the implementation - the "Files" tab shows that.
Reducing option allocations in FSharpFindUsagesService.onSymbolFound and showing benchmark data would tell the WHY (because Option module is inlined, so often there is not much to be saved)