`TextCommandBarFlyout` has no icon for Select all

### Describe the bug

All items in `TextCommandBarFlyout` seem to have an icon, except for Select all, which feels a bit inconsistent.

### Why is this important?

Consistent UX

### Steps to reproduce the bug

1. Create a `TextBox`
2. Type something into it
3. Right-click
4. **Observe the issue**

### Actual behavior

No icon in Select all

### Expected behavior

Should have an icon

### Screenshots

### NuGet package version

WinUI 3 - Windows App SDK 1.8.3: 1.8.251106002

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

Start by reproducing the issue with a TextBox and right-clicking to open TextCommandBarFlyout. Locate the implementation and the existing command icon definitions, then compare Select all with the other items. Done means Select all displays an icon consistently with the other commands.

Written by the indexing model from the issue text.