SecureField

[kaascevich]

This PR adds SecureField, which is simply TextField but everything shows up as a dot. Implemented and working on all backends. (There is a quirk on WinUIBackend where the field doesn’t show up until the first rerender -- I have absolutely no idea where this bug could be coming from and so I’m saving it for Later™.)

Resolves #247.

[stackotter]

This might help fix the WinUI issue;

swift-cross-ui/Sources/WinUIBackend/WinUIBackend.swift

Line 631 in b2d021b

} else if let textField = widget as? WinUI.TextBox, textField.padding == noPadding {

(it’s what I did to fix a basically identical issue with TextField widgets)

[kaascevich]

That works, thanks! (I just replaced TextBox with TextBoxProtocol)

[stackotter]

Looks like you need to add default implementations to AppBackend to satisfy the CI (and implement DummyBackend support)

[stackotter]

I haven't reviewed the backend code because it'll probably change as a result of this set of comments; just focussed on the common SCUI implementation.