Fix greatgun mappings & mouse buttons, add multimouse/lightgun

[StormedBubbles]

Hello,

This is almost identical to my lr-mame2015 pull request since 2015 and 2016 largely share the same code. Here is what I changed:

• Change greatgun's input mappings to match current MAME.
• Fix up the mouse buttons. The right mouse button appeared to not be activated correctly, while the middle mouse button was missing entirely. Now, each mouse has 3 unique buttons.
• Add lightgun mode. MAME will recognize mouse movement as gun axes in this mode. In addition, the Libretro "Gun Trigger" and "Gun Aux A" will be recognized as the first two gun buttons by MAME. Finally, the cursor will be glued to the top-left corner of the screen when it hits the edge of the screen (helping the behavior of offscreen reload), and the Libretro "Gun Reload" input will emulate an offscreen shot.
• Add multimouse/lightgun. Players can use up to 4 of either.

The "XY device (Restart)" option replaces the option that enables the mouse and allows the user to switch among "none," "lightgun," and "mouse." As mentioned in my 2015 pull request, it would be better to make this option not require a restart. I wasn't able to figure that out, so please feel free to edit or make suggestions on how this could be done!

[StormedBubbles]

I forgot to mention that this will resolve issues #45, #50, and #54.

[Colgaton]

Is there a plan to merge them?

[StormedBubbles]

Hi,

I have been using this on my own build (Raspberry Pi 4B) since I submitted the PR. I don't think there are any issues introduced by the additions.

I wasn't able to extend the player count past 4 for some reason. Compiling worked, but the emulator would crash without an indication of what the issue was. I'm guessing the issue had something to do with input descriptors because lr-mame had a similar issue that was resolved a while ago.

In the future, I can add in additional gun buttons (Aux B, Aux C, Gun Start/Select, Gun D-Pad) if desired. I will leave that for a separate PR.