refactor key scans and add gamepad button/axes scans

[harbdog]

• Leverage the ebitengine "just released" inpututil functions to simplify existing keyboard key scanning and add gamepad and mouse button scanning capability.
• Add gamepad axes scanning capability.
• Example axes scanning with moveable "character" added to _examples/remap.

[harbdog]

@quasilyte what are your thoughts on this refactored approach to key scanning? I'm also hoping to later add ability to scan for mouse buttons, maybe even gamepad axes.

[quasilyte]

I do like the idea to make it better! I only had a limited use of it to implement the in-game key rebinding. The lack of the mouse scanning, for instance, was noticeable even there.
So please go ahead :D

[quasilyte]

Ping me when it's ready for review/merge.

[harbdog]

I've gotten mouse wheel working as well, next up is figuring out mouse axes since this does not appear to be a "Key" managed by ebitengine-input at the moment like other axes such as gamepad sticks.

[harbdog]

@quasilyte I think it's in a good place now, I also went ahead and added mouse move as a "key" that can be bound to an action and scanned for remapping :)

[harbdog]

I went back and improved the example after trying to translate it to how my game uses scanning and finding it needed to be made clearer on toggling the different scan types independently.

[harbdog]

Back to draft, found an issue where my game using ebitenui is not picking up mouse axes events like the example was, so need to figure that out first.

[harbdog]

Figured it out, it was a problem in my game input system setup where I was de-referencing pointers somewhere I shouldn't have and it caused the Handler's System.cursorPos to not be updated on the correct reference: pixelmek-3d/pixelmek-3d@ed47c6c