Add option to toggle unused declarations analyzer (dotnet#4074)

* Add option to toggle unused declarations analyzer

* Better name and handle registering code fixes.

This will ensure that if someone uses warnon:1182, we won't suggest
fixes if they've turned off the feature.

Author: cartermp

CodeFix/RenameUnusedValue.fs

@@ -47,6 +47,9 @@ type internal FSharpRenameUnusedValueCodeFixProvider
 
     override __.RegisterCodeFixesAsync context : Task =
         asyncMaybe {
+            // Don't show code fixes for unused values, even if they are compiler-generated.
+            do! Option.guard Settings.CodeFixes.UnusedDeclarations
+
             let document = context.Document
             let! sourceText = document.GetTextAsync()
             let ident = sourceText.ToString(context.Span)

Diagnostics/UnusedDeclarationsAnalyzer.fs

@@ -100,6 +100,8 @@ type internal UnusedDeclarationsAnalyzer() =
 
     override __.AnalyzeSemanticsAsync(document, cancellationToken) =
         asyncMaybe {
+            do! Option.guard Settings.CodeFixes.UnusedDeclarations
+
             do Trace.TraceInformation("{0:n3} (start) UnusedDeclarationsAnalyzer", DateTime.Now.TimeOfDay.TotalSeconds)
             do! Async.Sleep DefaultTuning.UnusedDeclarationsAnalyzerInitialDelay |> liftAsync // be less intrusive, give other work priority most of the time
             match getProjectInfoManager(document).TryGetOptionsForEditingDocumentOrProject(document) with

Options/EditorOptions.fs

@@ -34,7 +34,8 @@ type QuickInfoOptions =
 type CodeFixesOptions =
     { SimplifyName: bool
       AlwaysPlaceOpensAtTopLevel: bool
-      UnusedOpens: bool }
+      UnusedOpens: bool 
+      UnusedDeclarations: bool }
 
 [<CLIMutable>]
 type LanguageServicePerformanceOptions = 
@@ -59,7 +60,8 @@ type internal Settings [<ImportingConstructor>](store: SettingsStore) =
               // See https://github.com/Microsoft/visualfsharp/pull/3238#issue-237699595
               SimplifyName = false 
               AlwaysPlaceOpensAtTopLevel = false
-              UnusedOpens = true }
+              UnusedOpens = true 
+              UnusedDeclarations = true }
 
         store.RegisterDefault
             { EnableInMemoryCrossProjectReferences = true