[WIIU Feature Request] USB HID mouse support.

Description

The Wii U prominently features several USB ports, with two on the face of the unit and two more on the back. RetroArch on Wii U currently supports USB keyboards, but not mice. Adding mouse support would be a huge improvement for the several cores which would benefit from mouse controls, like ScummVM, DOSBox, the various Snes9x flavors (Mario Paint!) and Genesis Plus GX.

There may be a greater issue underlying this one, depending on how mice work in RetroArch: RA's emulated touch screen mouse support currently appears fairly limited. gblues recently fixed the feature in #11191, but while it works well in ScummVM, as far as I can tell it isn't compatible with the DOSBox, SNES or Mega Drive cores. I'm not sure if these would need to work with emulated mouse support before they would work with actual mice or not.

Either way, the current lack of mouse support leaves many games unplayable and others much less playable than they might otherwise be.

EDIT: It was just brought to my attention that not everybody knows the extent to which mouse controls saw adoption in SNES and other games. The Wikipedia article on the Super NES Mouse lists about 70 titles with mouse support, among them titles such as Arkanoid, Cameltry, Cannon Fodder, Civilization, Doom, Lord of the Rings, Jurassic Park, Lemmings, Mario & Wario, Nobunaga's Ambition, Populous, SimAnt, Terminator, Wolfenstein, Wonder Project J.

Taking note of the first-person shooters in the above SNES list, RetroArch on Wii U also has cores for Wolfenstein 3D, Doom, Quake and Quake 2. Other cores which could potentially benefit from mouse support include the various Commodore computer cores, the Hatari Atari ST core, the Amstrad CPC cores, the various PC Engine/CD/SuperGrafx cores, the Sinclair computers ... most of these didn't use mice as their primary method of input, but there are mouse accessories for a lot of platforms that can be emulated within RetroArch on Wii U, which would be well served by support for real mice.

The issue names no files or tests. Start by examining RetroArch's Wii U input handling and the related emulated touch-screen work in #11191, then determine how USB HID mice should reach the affected cores. Done means real USB mice work reliably across the listed mouse-capable cores without regressing keyboard or existing emulated mouse support.