fix: ensure any property editor UIs save their initial value on the context

[iOvergaard]

Description

This ensures that if, say, a textarea is saved with "rows=10" without touching the input box at all

Before

After

How to test

1. Create a new data type
2. Select textarea
3. Hit save
4. Verify that the default configuration is saved, i.e. rows=10

[iOvergaard]

I noticed that if the value is undefined, then the alias will be saved sort of without a value. We need to make sure that scenario works on the server.