libinput.h/evdev.c: Add definitions for LIBINPUT_LED_COMPOSE and LIBINPUT_LED_KANA

Blinkenlights status of The Great Five(Num Lock,Caps Lock,Scroll Lock, Compose, Kana (Lock)):

• Base Linux support - All 5 LEDs are exposed and controllable in /sys
• libinput which has a PR here, 1.26 released with the patch
• xf86-input-evdev which has a PR here, will be in some version past 2.10.6
• libxkbcommon which has a PR here, marked for 1.8.0 release
• xf86-input-libinput which has a PR here - will be in some version past 1.4.0
• GTK (wayland) has a PR here
• kwin which has a PR here
  • plasma-wayland-protocols which has a PR here
• mutter has a PR here
• wlroots has a PR here
• weston has a PR here
• xkeyboard-config needs some work, as neither Scroll Lock, Compose or Kana are bound by default.
  • Scroll Lock support - seems (results in broken keyboard backlight) - very - broken. Has a recent xkeyboard-config PR. Unbound by default in xkeyboard-config.
  • Compose support
  • Kana (Lock) support

LED testing done using VIAL(QMK fork).

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Fixes #818 (closed)

This probably should have tests added in test/test-keyboard.c?
I am not sure how to write them.

~~Is there a reason to implement only the first five keys, or would it be a good idea to do the rest too?~~

#define LED_NUML		0x00
#define LED_CAPSL		0x01
#define LED_SCROLLL		0x02
#define LED_COMPOSE		0x03
#define LED_KANA		0x04
#define LED_SLEEP		0x05
#define LED_SUSPEND		0x06
#define LED_MUTE		0x07
#define LED_MISC		0x08
#define LED_MAIL		0x09
#define LED_CHARGING		0x0a
#define LED_MAX			0x0f
#define LED_CNT			(LED_MAX+1)

EDIT: No, it's not a good idea, 1-5 is official HID spec
Fun fact, the 1.0 spec is from 1996, meaning I am implementing/fixing a feature for which the spec is older than me.