Fix font face keyboard selection crash

[danyalahmed1995]

Summary

Fixes a crash in the Settings UI font face control when selecting a font suggestion with the keyboard and pressing Enter.

The font face AutoSuggestBox path was explicitly unfocusing the box after a chosen suggestion was submitted. During the keyboard suggestion commit path, that Focus(FocusState::Unfocused) call can trigger a WinUI/XAML crash before the settings model update completes.

This change avoids explicitly unfocusing the AutoSuggestBox in the chosen-suggestion path and instead commits the selected font and moves focus to the parent container.

Fixes #20245.

Validation

Manually validated with a local CascadiaPackage Debug x64 build:

• Reproduced the crash before the fix.
• Opened Settings → Defaults → Appearance → Font face.
• Typed a partial font name.
• Used arrow keys to select a suggestion.
• Pressed Enter.
• Verified Terminal no longer crashes.
• Verified the selected font is applied and Save works.

Also checked:

git diff --check
git diff --numstat