Add ability to underline variables in the editor that are reassigned.

src/Analyzers/CSharp/Analyzers/UseLocalFunction/CSharpUseLocalFunctionDiagnosticAnalyzer.cs

@@ -229,7 +229,7 @@ private static bool CanReplaceAnonymousWithLocalFunction(
  if (identifierName.Identifier.ValueText == local.Name &&
  local.Equals(semanticModel.GetSymbolInfo(identifierName, cancellationToken).GetAnySymbol()))
  {
- if (identifierName.IsWrittenTo())
+ if (identifierName.IsWrittenTo(semanticModel, cancellationToken))
  {
  // Can't change this to a local function if it is assigned to.
  return false;

src/Analyzers/CSharp/Analyzers/UsePatternMatching/CSharpAsAndNullCheckDiagnosticAnalyzer.cs

@@ -194,7 +194,7 @@ private void SyntaxNodeAction(SyntaxNodeAnalysisContext syntaxContext)
  // Check if this is a 'write' to the asOperand.
  if (identifierName.Identifier.ValueText == asOperand?.Name &&
  asOperand.Equals(semanticModel.GetSymbolInfo(identifierName, cancellationToken).Symbol) &&
- identifierName.IsWrittenTo())
+ identifierName.IsWrittenTo(semanticModel, cancellationToken))
  {
  return;
  }