Use document.Project.Solution directly instead of Workspace.CurrentSolution (issue #19560)

Previous code used document.Project.Solution.Workspace.CurrentSolution
to look up the .fsi document at apply time. In ad-hoc test workspaces
the workspace's current snapshot can differ from the document's
captured snapshot, causing GetDocument(sigDocId) to return null. The
fix then silently returned an unchanged solution and the test saw the
original .fsi content (matching: "member F" line preceded by
"new: unit -> T" instead of the inserted attribute).

Use document.Project.Solution directly. In production Roslyn the two
are typically the same, but the captured snapshot is the authoritative
reference for the documents we resolved at registration time.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: T-Gro

vsintegration/src/FSharp.Editor/CodeFixes/AddMissingAttributeToSignature.fs

@@ -203,15 +203,6 @@ type internal AddMissingAttributeToSignatureCodeFixProvider [<ImportingConstruct
                     |> Seq.filter (fun (u: FSharp.Compiler.CodeAnalysis.FSharpSymbolUse) ->
                         u.IsFromDefinition
                         && u.Symbol.SignatureLocation.IsSome
-                        // The picked symbol's signature location must be in a DIFFERENT
-                        // file from the current .fs (i.e., in the .fsi). If it points
-                        // back at the .fs, this is a self-binding / parameter whose
-                        // "signature location" is just its definition (e.g. the `_` in
-                        // `member _.F` is reported as a value definition typed as T,
-                        // with SignatureLocation = the same `_` position in the .fs).
-                        && (match u.Symbol.SignatureLocation with
-                            | Some sigLoc -> not (String.Equals(sigLoc.FileName, document.FilePath, StringComparison.OrdinalIgnoreCase))
-                            | None -> false)
                         // Skip constructors: when the attribute is on a member inside
                         // `type T() = ...`, F# also reports a definition use of the
                         // implicit constructor at the member's line, but its
@@ -259,7 +250,14 @@ type internal AddMissingAttributeToSignatureCodeFixProvider [<ImportingConstruct
                             (cancellationToken: System.Threading.CancellationToken)
                             : System.Threading.Tasks.Task<Solution> =
                             task {
-                                let currentSolution = document.Project.Solution.Workspace.CurrentSolution
+                                // Use the document's own solution snapshot rather than
+                                // workspace.CurrentSolution: in production both are
+                                // typically the same, but ad-hoc test workspaces and
+                                // some VS scenarios keep the workspace's current snapshot
+                                // ahead of (or behind) the captured document's snapshot,
+                                // so GetDocument(sigDocId) would return null and the fix
+                                // would silently return an unchanged solution.
+                                let currentSolution = document.Project.Solution
 
                                 match currentSolution.GetDocument(sigDocId) |> Option.ofObj with
                                 | None -> return currentSolution