Extract local function: Variable shadowing prior CSharp 8

[MaStr11]

Fix #55031

C# 8 allows shadowing of variables by local function parameters. The Extract local function refactoring takes this for granted. The following code is causing CS0136 (A local variable named 'var' cannot be declared in this scope because it would give a different meaning to 'var', which is already used in a 'parent or current/child' scope to denote something else) in C# 7.3 and older:

Before

        static void Main(string[] args)
        {
            var f = "{0}";
            string.Format(f, ""); // Extract local function
        }

After

        static void Main(string[] args)
        {
            var f = "{0}";
            NewMethod(f);

            void NewMethod(string f) // Valid in C#8 but causes CS0136 in C#7.3.
            {
                string.Format(f, "");
            }
        }

[MaStr11]

@CyrusNajmabadi What is the expected behavior:

Name the function parameter f1

        static void Main(string[] args)
        {
            var f = "{0}";
            NewMethod(f);

            void NewMethod(string f1)
            {
                string.Format(f1, "");
            }
        }

Capture f

        static void Main(string[] args)
        {
            var f = "{0}";
            NewMethod();

            void NewMethod()
            {
                string.Format(f, "");
            }
        }

[MaStr11]

f is causing CS0136 in C# 7.3. The refactoring should either name the parameter differently or capture f.

[CyrusNajmabadi]

Capturing or renaming both seem reasonable. I'd like the refactoring to offer both options.

[ryzngard]

#55446 has the fix to rename the variable here by default. If we want to capture as a different option we should file an issue for adding that

[MaStr11]

#55446 uses the capturing approach. I'm going to close this PR in favor of #55446 because it is almost done and it fixes the issue. If anyone sees value in adding the "pass parameters (with renaming if before C# 8 or only offer passing if C# 8 and above)", that should be added after #55446 is merged. But I agree, that this is a separate issue.

[MaStr11]

Closed in favor of #55446