Switch ISymbolExtensionsTests to SymbolFinder.FindSymbolAtPositionAsync

This was directly calling internal helpers that I'm potentially going to
have to refactor, and this didn't need any special behavior over our
public helper for this.

src/EditorFeatures/Test2/Extensions/ISymbolExtensionsTests.vb

@@ -3,6 +3,7 @@
 Imports System.Threading
 Imports System.Threading.Tasks
 Imports Microsoft.CodeAnalysis
+Imports Microsoft.CodeAnalysis.FindSymbols
 
 Namespace Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces
     <[UseExportProvider]>
@@ -15,12 +16,8 @@ Namespace Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces
                 Dim cursorPosition = cursorDocument.CursorPosition.Value
                 Dim document = workspace.CurrentSolution.GetDocument(cursorDocument.Id)
 
-                Dim tree = Await document.GetSyntaxTreeAsync()
-                Dim commonSyntaxToken = Await tree.GetTouchingTokenAsync(cursorPosition, Nothing)
-
                 Dim semanticModel = Await document.GetSemanticModelAsync()
-                Dim symbol = semanticModel.GetSemanticInfo(commonSyntaxToken, document.Project.Solution.Workspace, Nothing).
-                                           GetAnySymbol(includeType:=False)
+                Dim symbol = Await SymbolFinder.FindSymbolAtPositionAsync(document, cursorPosition)
                 Dim namedTypeSymbol = semanticModel.GetEnclosingNamedType(cursorPosition, CancellationToken.None)
 
                 Dim actualVisible = symbol.IsAccessibleWithin(namedTypeSymbol)