Support stateful popovers

[raysarebest]

Let's say I have a popover that looks like this:

import Popovers
import SwiftUI

struct BasicView: View {
    @State var present = false

    var body: some View {
        ExampleRow(
            image: "square",
            title: "Basic",
            color: 0x00AEEF
        ) {
            present.toggle()
        }
        .popover(present: $present) {
            TimedRenderingView()
                .background(.thinMaterial)
        }

    }
    
    struct TimedRenderingView: View {
        @State private var data = ["Example"]
        let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
        
        var body: some View {
            VStack {
                ForEach(data, id: \.self) { line in
                    Text(line)
                }
            }
            .onReceive(timer) { _ in
                data = Array(repeating: "Example", count: .random(in: 1...10))
            }
        }
    }
}

Currently, once the popover is presented, it will never be updated, even as the data changes. This PR adds support for re-rendering the popover view when SwiftUI decides it's appropriate, such as when one or more of its state, binding, or environment properties change. This represents a partial fix for #72, specifically for cases where popover views maintain some kind of internal properties to signal the need for a re-render

This work was done as part of my day job at Chariot Solutions, LLC to help support projects for ourselves and our clients