Added support for alert without title

[fhasse95]

This PR changes the alert view modifier to match the iOS behavior if no / an empty title is used.

Example SwiftUI code to test the changes:

struct ExampleView: View {
    @State private var showAlert: Bool = false
    
    var body: some View {
        Button("Show Alert") {
            self.showAlert = true
        }.alert("", isPresented: self.$showAlert) {
            Button("Yes") { }
            Button("No") { }
            Button("Cancel", role: .cancel) { }
        }
    }
}

iOS:

Android (Before):

Android (After):

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[marcprux]

Looks great overall, and thanks for the screenshots! Just one question about the change to an optional init Text parameter…