Port UWP taskbar behavior when fullscreen to Win32 apps

# Proposal: [Port UWP taskbar behavior when fullscreen to Win32 apps]

## Summary

If a UWP app is in full screen if I swipe up from the bottom part of the screen with touch or otherwise with a touchpad/mouse I just hover the bottom part of the screen.
In Win32 apps nothing happens. The only way to switch to apps is using multitasking view, which is quite annoying.
Another useful feature of this uwp feature is the ability to retrieve the title bar analogously by swiping down from the upper part of the screen or putting the mouse hover on top.
This could be invoked with the useful shortcut Win+Shift+Enter like in UWP apps so that you can also manually opt it in

## Rationale

* Having the same behaviour in Win32/UWP apps is ok for the purpose of Project Reunion
* Being able to switch among apps or just check the time or info on taskbar would be made definitely easier and with basically no drawback

## Scope

| Capability | Priority |
| :---------- | :------- |

## Important Notes

## Open Questions

Will this behavior cause problems to games where the taskbar could be popping-out continuously?
My idea is to make this one the default behavior, even if an option to disable it should be present. For those who continue to argue about games, I just think that they aren't the main usage of WinAppSDK, that I think is instead new generation WinUI 3 apps

The proposal names no implementation files, entry points, or tests. Start by reviewing the Windows App SDK roadmap linked in the issue and examining how fullscreen Win32 and UWP taskbar behavior differ. Before implementation, clarify the API, default behavior, game interaction, and opt-out scope; completion would require an agreed design and validation of the resulting taskbar behavior.

Written by the indexing model from the issue text.