Window close button does not fill with main window

### Describe the bug

Window close button have padding right in main window

### Steps to reproduce the bug

```
_mainWindow.ExtendsContentIntoTitleBar = true
_mainWindow.SetAdjustBar(GetCurrentTheme());
```

### Expected behavior

Remove right padding for Window Close button

### Screenshots


### NuGet package version

WinUI 3 - Windows App SDK 1.5.6: 1.5.240802000

### Windows version

Windows 10 (21H1): Build 19043

### Additional context

_No response_

Reproduce the issue using _mainWindow.ExtendsContentIntoTitleBar = true and _mainWindow.SetAdjustBar(GetCurrentTheme()) on WinUI 3 with Windows App SDK 1.5.6. Trace the title-bar and close-button layout involved in that configuration; done means the Window Close button has no unwanted right padding and fills the main window edge.

Written by the indexing model from the issue text.