[ipa picker] Vowel diacritic input using default type assist

[phequa]

Adding diacritics to the letters a, u, and y through the ! shortcut then selecting any of the number options deletes the vowel and only outputs the diacritic.
Same thing for a but for accessing the diacritics through the @ shortcut.

I think it's because the some symbols with the voiceless diacritic can only backspaced as a whole.