extract MainTabView

Start to clean ContentView up a bit.

We need it to be cleaner before we introduce the SetupView

Signed-off-by: William Casarin <jb55@jb55.com>

damus/Views/SetupView.swift

@@ -0,0 +1,20 @@
+//
+//  SetupView.swift
+//  damus
+//
+//  Created by William Casarin on 2022-05-18.
+//
+
+import SwiftUI
+
+struct SetupView: View {
+    var body: some View {
+        Text(/*@START_MENU_TOKEN@*/"Hello, World!"/*@END_MENU_TOKEN@*/)
+    }
+}
+
+struct SetupView_Previews: PreviewProvider {
+    static var previews: some View {
+        SetupView()
+    }
+}