IsEnabled & IsReadOnly two-way binding propergation issues

[DevFromDownUnder]

In #639 we updated to two-way bindings.

While testing with a separate project I worked out that the way MAUI propergates the IsEnabled and IsFocused fields has issues with this.

I suggest reverting those two back to one-way bindings.

Should never really be updated the IsEnabled for a TextField with TextField.Entry.IsEnabled anyway, I originally just added them to match.