Classify each Find All References line while the search runs

[xperiandri]

Description

Find All References lists each reference with its line classified. C# and VB classify that line as they find the reference and hand it over. F# handed nothing, so after the search the window asked the F# classification service for the syntactic and semantic classification of every line again, one reference at a time. For a file that is not open, the semantic part comes from a whole-file classification kept for five seconds, so a long result list can outlive it and pay for it again.

dotnet/roslyn#85281 adds a FSharpSourceReferenceItem constructor that takes the classified line. This fills it while the search still has the checked file at hand.

ClassifiedReferenceLine classifies the line the way Roslyn's ClassifiedSpansAndHighlightSpanFactory and ClassifierHelper do:

• the line runs from its first non-whitespace character to its end;
• spans are sorted, clipped to the line, and a span overlapping the one before is dropped;
• semantic spans win over the syntactic spans they overlap;
• gaps are filled with plain text.

The references found in C# and VB projects are still classified by the window, which asks Roslyn.

Checklist

• Test cases added: ClassifiedReferenceLineTests checks that an indented reference line is covered from its first non-whitespace character to its end, that the reference keeps its semantic classification, and that a literal keeps its syntactic one.
• Performance benchmarks added in case of performance changes
• Release notes entry updated

Draft

This cannot build until dotnet/roslyn#85281 has flowed. Against a local build of dotnet/roslyn#85280 and #85281 together, the affected FSharp.Editor.Tests classes pass (145): Navigate To search, persistent cache, loading search and multi-target search, Find All References and multi-target Find All References, semantic classification, Copilot mentions, and the new tests.

🤖 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

[xperiandri]

Suggested change

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

[xperiandri]

Split out as #20534 — this line isn't touched by this PR.

[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.