bug(windows): compatibility: Notepad with Vietnamese refuses to accept some combinations

**Describe the bug**

If I have a custom keyboard layout registered with vi-vn that tries to emit ẃ U+0077 U+0301, Notepad will not accept that combination. It accepts the U+0077 and then makes a beep sound and refuses to take the combining diacritic. Many other applications and contexts work (Wordpad doesn't) - e.g. Windows Search accepts the combination, as does Word.

If I register the exact same keyboard with an en language code, then Notepad accepts the combination.

Notepad should not be blocking character combinations like this. (I can paste it in, no problem)

Note: this is not a bug in Keyman.

Feedback Hub link: https://aka.ms/AA6rjn7

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**Keyman Desktop:**
- OS: Windows 10 1903
- Keyman version: 12.0
- Target Application: Notepad, Wordpad