Add facilities for StreamRendering

[Tarmil]

• For stream rendering SSR: add class StreamRenderingComponent<'model>.

  Example use:

  type Model = { text: string }
  
  type MySlowComponent() =
      inherit StreamRenderingComponent<Model>()
  
      override _.InitialModel = { text = "loading..." }
  
      override _.LoadModel(initialModel) = task {
          do! Task.Delay (TimeSpan.FromSeconds 2) // Simulate slow loading
          return { initialModel with text = "loaded!" }
      }
  
      override _.Render(model) =
          div { $"Stream-rendered component is {model.text}" }
  
  let index = doctypeHtml {
      head { ... }
      body {
          comp<MySlowComponent>
          boleroScript
      }
  }

  Note: unfortunately, it's not possible to create a function that would take initialModel, loadModel and render as arguments and instantiate the component, similarly to lazyComp. This would involve passing function-typed parameters to the component, but stream rendering requires serializable parameters.

• For stream rendering Elmish program:

  • Program.mkStreamRendering, similar to Program.mkProgram except instead of an init function, it takes an initial model and a load function that returns a task.
  • Program.mkSimpleStreamRendering, similarly based on Program.mkSimple.

  Example use:

  type Model = { text: string }
  
  type Msg = ...
  
  let update msg model = ...
  
  let init = { text = "loading..." }
  
  let load initialModel = task {
      do! Task.Delay (TimeSpan.FromSeconds 2) // Simulate slow loading
      return ({ model with text = "loaded!" }, Cmd.none)
  }
  
  let view model dispatch =
      div { $"Stream-rendered component is {model.text}" }
  
  type MySlowComponent() =
      inherit ProgramComponent<Model, Msg>()
  
      override _.Program =
          Program.mkStreamRendering init load update view
  
  
  let index = doctypeHtml {
      head { ... }
      body {
          // Also works with InteractiveWebAssemblyRenderMode.
          // Needs prerender = false, otherwise the initial model will show up again while the dynamic page runs load.
          comp<MySlowComponent> { attr.renderMode (InteractiveServerRenderMode(prerender = false)) }
          boleroScript
      }
  }