Proposal: default project improvements

# Proposal: default project improvements

## Summary
The current project template for a WinUI3 app is lacking a lot of issues. I recently created a new project which I wanted to use for a demo. It is strange that I had to add so many things before I could use it. These should be out of the box.

In this proposal I will show all the things I think are missing or wrong in the current template.

## Scope

| ID | Capability | Priority |
| :------- | :---------- | :------- |
| 1 | Visual Assets - Place the Visual Assets in a `Tiles` subfolder folder of the `Assets` folder | Must |
| 2 | Visual Assets - Remove unused tiles | Must|
| 3 | ~~Visual Assets - Add an Icon.ico and set it on the Window~~ | ~~Must~~ |
| 4 | ~~MainWindow - Add MicaBackdrop~~ | ~~Must~~ |
| 5 | ~~MainWindow - Add the new TitleBar~~ | ~~Must~~ |
| 6 | MainWindow - Add a Minimum size | Must |
| 7 | ~~MainWindow - Replace the 'Click Me' Button for a Frame and navigate to a MainPage~~ | ~~Must~~ |
| 8 | ~~Introduce a MainPage with a Counter~~ | ~~Should~~ |
| 9 | Folders - Add a GlobalUsings.cs | Could |
| 10 | Folders - Introduce a Views folder | Could |
| 11 | Folders - Default Styles.xaml Resource Dictionary | Should |
| 12 | Folders - Default Themes.xaml Resource Dictionary | Should |

- 'Must' implies that the feature should not ship without this capability.
- 'Should' is something we should push hard for, but is not absolutely required to ship.
- 'Could' is a nice-to-have; a good stretch goal that isn't painful if we don't achieve it.
- 'Won't' is a clear statement that the proposal/feature will intentionally not have that capability.

## Visual Assets

### Place the Visual Assets in a `Tiles` subfolder folder of the `Assets` folder

Currently all tiles are placed in the `Assets` folder itself. I often create extra folders too like `Fonts`, `Sounds`, `Images` but they don't have to be there in the template.

The `Package.appxmanifest` should point to this folder.


### Remove unused tiles

The `Wide310x150Logo.png` and `SplashScreen.png` can be removed from the project. They are not used in WinUI.

### Add an Icon.ico and set it on the Window

A WinUI3 should have an Icon file otherwise the app will get a blue background color in the TaskBar. It took me hours to find a solution for it. Thanks to many on the [Discord](https://discordapp.com/channels/372137812037730304/671870147354427422/1344272668462940191) group.

In the `Assets/Tiles` folder I would like to have an `Icon.ico` file with the `Build Action` set to `Content`. In the 'App.xaml.cs' file you need to call `SetIcon()`.

For this demo I converted a Smiley.png into an Icon file using the [`Simple Icon File Maker'](https://apps.microsoft.com/detail/9NS1BM1FB99Z?hl=en-us&gl=US&ocid=pdpshare) app from Joe Finney.

```cs
///
/// Invoked when the application is launched.
///
/// Details about the launch request and process.
protected override void OnLaunched(Microsoft.UI.Xaml.LaunchActivatedEventArgs args)
{
m_window = new MainWindow();

AppWindow appWindow = GetAppWindow(m_window);
appWindow.SetIcon("Assets/Tiles/Icon.ico");

// This requires WinUIEx NuGet Package
// m_window.SetIcon("Assets/Icons/Icon.ico");

m_window.Activate();

}

private static AppWindow GetAppWindow(Window window) {
IntPtr hWnd = WindowNative.GetWindowHandle(window);
WindowId wndId = Win32Interop.GetWindowIdFromWindow(hWnd);
return AppWindow.GetFromWindowId(wndId);
}
```


## MainWindow

### Add MicaBackdrop

```xml

```

The ugly white background is now gone. And you have Mica.


### Add the new TitleBar

If you are using WinAppSDK version 1.7 (currently in preview) you could use the new TitleBar control in your Window

```xml

```

The Title of the TitleBar is databound to the Title property of the window. The IconSource is set to the StoreLogo.png.

You also have to set the ExtendsContentIntoTitleBar and the Title, so I changed the constructor of the MainWindow into this. Using the `Package.DisplayName` is better than using some hard coded string.

```cs
public sealed partial class MainWindow : Window {
public MainWindow() {
this.InitializeComponent();

Title = global::Windows.ApplicationModel.Package.Current.DisplayName;
ExtendsContentIntoTitleBar = true;
}
}
```

### Add a Minimum size
Add a solution to the MainWindow to set the minimum size. Nobody wants this.


### Replace the 'Click Me' Button for a Frame and navigate to a MainPage

I think the currently used 'Click Me' button is quite useless. I think you should not have any XAML controls in a Window. Windows are limited. They cannot have Resources. In UWP apps we are used to write XAML in Pages, by default a `MainPage.xaml`. That is what we should do in WinUI too. We can also use the BackButton logic of the TitleBar to make that easier too.

```xml

```

In the constructor of the `MainWindow` you can navigate to a `MainPage` and also have the `BackRequested` handler.

```cs
public sealed partial class MainWindow : Window {
public MainWindow() {
this.InitializeComponent();

Title = global::Windows.ApplicationModel.Package.Current.DisplayName;
ExtendsContentIntoTitleBar = true;

RootFrame.Navigate(typeof(MainPage));
}

private void TitleBar_BackRequested(TitleBar sender, object args) {
if (RootFrame.CanGoBack) {
RootFrame.GoBack();
}
}
}
```

This results in a `Back` button in the `TitleBar` if back navigation is possible.


## Introduce a MainPage with a Counter

We need a MainPage and it needs something more than only a `Click Me` button. In Blazor and Maui there is a Counter page. Maybe we should implement that too.

## Folders

### Add a GlobalUsings.cs

We don't have ImplicitUsings for WinUI apps like ASP.NET, WPF or Windows Forms. Let's create a GlobalUsings.cs file to mimic this behavior.

```cs
global using Microsoft.UI.Xaml;
global using Microsoft.UI.Xaml.Controls;
global using Microsoft.UI.Xaml.Controls.Primitives;

global using Windows.System;
```

### Introduce a Views folder

All view related items (Windows, Pages, Resources, Controls, Dialogs) should be placed in a Views folder. Preferably with subfolders for each type.


### Default Styles.xaml Resource Dictionary

The project could have a `Styles.xaml` resource dictionary which is merged from the `App.xaml` file. Having a separate file for it learns unexperienced developers to use styling and the use of Resource Dictionaries.


### Default Themes.xaml Resource Dictionary

Add a Themes.xaml resource dictionary and reference it from the App.xaml. If new developers know that this exists, they will start using it (hopefully).

```xml

```

## Important Notes
I'm quite sure that there are many other improvements to be made. Is my priority ok? Please react on this proposal to get them all discussed.

Start by reviewing the current WinUI3 project template, especially Package.appxmanifest, App.xaml.cs, MainWindow, App.xaml, and the proposed MainPage. Compare the listed visual assets, window, navigation, folder, and resource-dictionary changes with the existing template. Done requires an agreed subset of this broad proposal and corresponding template updates.

Written by the indexing model from the issue text.