[LVGL] Allow editor to show UI past display limits

[zalexzperez]

When developing a UI for small displays, if the whole content doesn't fit into the display area at once (e.g. a long list of elements), the UI quickly becomes hidden making it difficult to see and work on the entire interface.

It would be beneficial to view the entire UI while still highlighting the display's visible area.
Specifically, when content is scrolled in any direction, the visible display area should move accordingly, rather than keeping the visible area fixed and moving the UI around.

[mvladic]

Implemented.

You can now use:

• ALT key + middle or right mouse button to scroll in both directions within LVGL widget
• ALT key + mouse wheel to scroll only vertically
• SHIFT+ALT key + mouse wheel to scroll only horizontally

[zalexzperez]

You're amazing. It works great !
It's better than the idea I had in mind.