IDE0051 false positive for extension referenced from another extension

**Version Used**:

VS 18.4.0

**Steps to Reproduce**:

```cs
static class Helpers
{
extension(User _this)
{
public bool IsUsed => _this.Helper();
}

// // warning IDE0051: Private member 'Helpers.Helper' is unused
private static bool Helper(this User _this)
{
return _this != null;
}
}

public class User
{
public void Test()
{
_ = this.IsUsed;
}
}

```

```xml

net10.0
enable
enable

true
preview-All
true

```
**Diagnostic Id**:

[Remove unused private member (IDE0051)](https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/style-rules/ide0051)

**Expected Behavior**:

no reports

**Actual Behavior**:

incorrect diagnostic reported

Start by reproducing the C# example with analyzer diagnostic IDE0051 enabled and confirm that Helper is reported as unused when referenced through the extension member. Trace the IDE0051 analysis for this extension-reference case; done means the sample produces no incorrect diagnostic while unused private members remain reported.

Written by the indexing model from the issue text.