Normalize all saved text to NFD

[myieye]

Describe the feature

We should normalize all text values that we persist to NFD.

See: https://community.software.sil.org/t/different-search-behavior-compared-to-dictionary-app/10839/4

Maybe we can implement this right into the JSON deserialization layer.

(In that case we could potentially also normalize to NFC when serializing)

Related to: #1860 (which needed to be reopened)