Fix AddReturnType refactoring throwing when file not in project

[Copilot]

Fix AddReturnType refactoring throwing on non-existent files

Problem: The AddReturnType refactoring throws when invoked on a file that's not yet known to the F# extension (e.g., file copied but project options not refreshed).

Solution: Wrapped the refactoring logic in a try-catch block to handle exceptions gracefully.

Changes Made:

• Understand the problem: exception thrown from GetFSharpParseAndCheckResultsAsync when file not in project
• Wrap the call to GetFSharpParseAndCheckResultsAsync in a try-catch in AddReturnType.fs
• Return early (no refactorings) when exception occurs
• Add test that actually simulates a document outside project context
• Format code
• Simplify exception handling (use wildcard pattern instead of redundant type tests)
• Commit changes

Files Changed:

1. vsintegration/src/FSharp.Editor/Refactor/AddReturnType.fs - Added try-catch block with wildcard pattern
2. vsintegration/tests/FSharp.Editor.Tests/Refactors/AddReturnTypeTests.fs - Improved test to create a document not in F# project options

Ready for merge - The fix is minimal and surgical, addressing exactly the issue described. The test now properly simulates the race condition scenario.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>AddReturnType refactoring occasionally throws</issue_title>
<issue_description>I cannot come up with a definitive repo but this sometimes happens when I just copy a file in the solution explorer.

Here is the stack trace:

System.Exception : The file 'C:\code\fsharp3\tests\benchmarks\FCSBenchmarks\CompilerServiceBenchmarks\GraphTypeCheckingBenchmarks - Copy.fs' was not part of the project. Did you call InvalidateConfiguration when the list of files in the project changed?
   at FSharp.Compiler.CodeAnalysis.IncrementalBuilder.GetSlotOfFileName(String fileName)
   at <StartupCode$FSharp-Compiler-Service>.$BackgroundCompiler.ParseAndCheckFileInProject@919-3.Invoke(FSharpOption`1 cachedResults)
   at FSharp.Compiler.BuildGraph.Bind@63-1.Invoke(T x)
   at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvokeNoHijackCheck[a,b](AsyncActivation`1 ctxt,b result1,FSharpFunc`2 userCode)
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.WorkspaceExtensions.CheckerExtensions.FSharpChecker-ParseAndCheckDocumentWithPossibleStaleResults@388-3(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.WorkspaceExtensions.CheckerExtensions.FSharpChecker-ParseAndCheckDocumentWithPossibleStaleResults@378(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.WorkspaceExtensions.CheckerExtensions.FSharpChecker-ParseAndCheckDocument@449(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.VisualStudio.FSharp.Editor.WorkspaceExtensions.Document-GetFSharpParseAndCheckResultsAsync@539(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async StartupCode$FSharp-Editor(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.CodeRefactorings.CodeRefactoringService.<>c__DisplayClass12_0.<GetRefactoringFromProviderAsync>b__0(<Unknown Parameters>)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at async Microsoft.CodeAnalysis.Extensions.IExtensionManagerExtensions.PerformFunctionAsync[T](<Unknown Parameters>)
```</issue_description>

<agent_instructions>AddReturnType refactoring (from vsintegration/src/FSharp.Editor/Refactor/AddReturnType.fs) throws then it is requested too fast, before the project options are refreshed.

Since this is annoying, lets make it more robust.
If the exception mentioned in this issue happens inside processing of the refactoring, it should just return () and not crash.

Locate existing refactoring tests and try to request refactoring for a non-existent file to verify it (non existent as in - F# extension not being aware of it)</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@vzarytovskii</author><body>
This likely happens because project system doesn't send us new command line options fast enough and we ask for tc results for file which is not in the project yet.</body></comment_new>
<comment_new><author>@T-Gro</author><body>
It can be if the VisualSVN modifies files on disk (e.g. a project file) faster then VS sends new project arguments to the F# extension.
When it comes to the refactoring service, a solution here can likely be making it more robust and delaying to a no-op in that situation (i.e. when refactoring provider asks for refactorings about a file that is not yet known to the extension, yield empty instead of throwing)</body></comment_new>
</comments>

• Fixes AddReturnType refactoring occasionally throws #16844

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