evdev: Add touchscreen mouse emulation and pressure support (thanks, Zach!). This also solves reports of this log message: "INFO: The key you just pressed is not recognized by SDL. To help get this fixed, please report this to the SDL forums/mailing list <https://discourse.libsdl.org/> EVDEV KeyCode 330" (EVDEV KeyCode 330 is BTN_TOUCH.) Fixes Bugzilla #4147.