Mobile friendly, for Launching

[Maksims]

Often, it is necessary to Launch application on mobile. But Scene selector UI is not mobile friendly at all. As well as Launch button.

Would be nice to make Editor a bit more mobile friendly, without full on integration, but at least:

1. Camera controls.
2. Simplify some panels.
3. Panel on left to be hidden, and shown using something like menu button.
4. Top controls on viewport, to not overlap each other.
5. When opening any panel like assets, hierarchy, inspector - make them to occupy full view, not just part of screen.
6. Most important, make scene viewable on mobile, and easy to launch with different settings.

[Maksims]

Bump on this.
Please check on analytics, if people open Editor on mobile devices - for every user that does, the experience is abysmal.

[willeastcott]

This issue is a really good example of why I think it'd be cool to open source the editor front-end. This type of issue normally gets neglected because we're tackling projects considered higher priority. But it should be fairly straightforward for the open source community to make improvements here.

It might not feel like we've made too much progress here, but @kpal81xd in particular has done a lot to clean up the Editor codebase lately. On top of that, he's developed new, reusable viewport elements like touch-friendly gizmos and camera controls which we do intend to integrate into the Editor (after SuperSplat and Model Viewer). So yeah, in my view, we should open source the front-end and continue to make relevant parts of the interface more mobile-friendly.

[willeastcott]

I think it's worth updating this issue on where we're at with this:

1. The Editor front-end is now open source
2. New gizmos are touch friendly
3. Camera controls in the Engine have gone through many iterations and are now mature but still haven't been integrated into the Editor. They are touch-friendly.
4. More of PCUI is now touch friendly. The TreeView is the main thing left to migrate to pointer events.
5. Some UI tweaking to work better on small screens is still needed.

But generally, we have made some good progress. Still more to do. But we haven't forgotten about this. And if anyone wants to attack any of this now that the front-end (and PCUI) is open source, be my guest. 😄

[willeastcott]

Related to #128