TextBlock render '\' as the Japanese currency symbol ¥ or Korean currency symbol ₩.

### Describe the bug

When using the ApplicationLanguages::PrimaryLanguageOverride(L"jp") or ApplicationLanguages::PrimaryLanguageOverride(L"ko") to set the app's languae, the TextBlock render the '\\' symbol as the Japanese currency symbol ¥ or Korean currency symbol ₩.

### Why is this important?

The GridView item in a XAML file:

...




using the ApplicationLanguages::PrimaryLanguageOverride(L"jp") or ApplicationLanguages::PrimaryLanguageOverride(L"ko") to set the app's languae, the TextBlock render the '\\' symbol as the Japanese currency symbol ¥ or Korean currency symbol ₩.

### Steps to reproduce the bug

1. Create a WinUI project.
2. The content of Main Window is GridView.
3. Use the TextBlock control to render the unicode string, like "\U+0031".
4. Use the ApplicationLanguages::PrimaryLanguageOverride(L"jp") or ApplicationLanguages::PrimaryLanguageOverride(L"ko") to set the app's languae.

### Actual behavior

### Expected behavior

### Screenshots

_No response_

### NuGet package version

WinUI 2.0.12

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

_No response_

No source file or test is identified. Start by reproducing the issue in a WinUI project with a TextBlock, a backslash-containing string, and ApplicationLanguages::PrimaryLanguageOverride set to "jp" and "ko"; done means the backslash renders consistently instead of as ¥ or ₩.

Written by the indexing model from the issue text.