[QuickAccent] Add Vietnamese (#40164)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
Adds support for Vietnamese in QuickAccent
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## PR Checklist

- [x] **Closes:** #36491
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [x] **Localization:** All end-user-facing strings can be localized
- [x] **Dev docs:** no need
- [x] **New binaries:** no need
- [x] **Documentation updated:** no need

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments
Vietnamese character set based of on
[Wikipedia](https://en.wikipedia.org/wiki/Vietnamese_alphabet)
<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed
Manually tested

src/settings-ui/Settings.UI/Strings/en-us/Resources.resw

@@ -3566,6 +3566,9 @@ Activate by holding the key for the character you want to add an accent to, then
   <data name="QuickAccent_SelectedLanguage_Turkish" xml:space="preserve">
     <value>Turkish</value>
   </data>
+  <data name="QuickAccent_SelectedLanguage_Vietnamese" xml:space="preserve">
+    <value>Vietnamese</value>
+  </data>
   <data name="QuickAccent_SelectedLanguage_Icelandic" xml:space="preserve">
     <value>Icelandic</value>
   </data>

src/settings-ui/Settings.UI/ViewModels/PowerAccentViewModel.cs

@@ -67,6 +67,7 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
             new PowerAccentLanguageModel("SR_CYRL", "QuickAccent_SelectedLanguage_Serbian_Cyrillic", LanguageGroup),
             new PowerAccentLanguageModel("SV", "QuickAccent_SelectedLanguage_Swedish", LanguageGroup),
             new PowerAccentLanguageModel("TK", "QuickAccent_SelectedLanguage_Turkish", LanguageGroup),
+            new PowerAccentLanguageModel("VI", "QuickAccent_SelectedLanguage_Vietnamese", LanguageGroup),
             new PowerAccentLanguageModel("CY", "QuickAccent_SelectedLanguage_Welsh", LanguageGroup),
         ];