Add key event label to Entry dump

When examining bugreports, it is inconvenient to have to look up
keycodes at the KeyEvent.java file or online in the documentation. When
checking the recent queue, it's nice to just have a printed value of a
specific key event.

Add KeyEvent::getLabel to the entry dump for KeyEntry.

Bug: 181096406

Test: press volume keys and then `adb shell dumpsys input`
Observe:
RecentQueue: length=10
    FocusEvent(hasFocus=false), age=14108ms
    FocusEvent(hasFocus=true), age=14099ms
    FocusEvent(hasFocus=false), age=14079ms
    FocusEvent(hasFocus=true), age=11936ms
    KeyEvent(deviceId=3, eventTime=477682467000, source=0x00000101, displayId=-1, action=DOWN, flags=0x00000008, keyCode=VOLUME_DOWN(25), scanCode=114, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=4160ms
    KeyEvent(deviceId=3, eventTime=477826780000, source=0x00000101, displayId=-1, action=UP, flags=0x00000008, keyCode=VOLUME_DOWN(25), scanCode=114, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=4015ms
    KeyEvent(deviceId=3, eventTime=479897187000, source=0x00000101, displayId=-1, action=DOWN, flags=0x00000008, keyCode=VOLUME_DOWN(25), scanCode=114, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=1945ms
    KeyEvent(deviceId=3, eventTime=480050313000, source=0x00000101, displayId=-1, action=UP, flags=0x00000008, keyCode=VOLUME_DOWN(25), scanCode=114, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=1792ms
    KeyEvent(deviceId=2, eventTime=480483397000, source=0x00000101, displayId=-1, action=DOWN, flags=0x00000008, keyCode=VOLUME_UP(24), scanCode=115, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=1359ms
    KeyEvent(deviceId=2, eventTime=480646721000, source=0x00000101, displayId=-1, action=UP, flags=0x00000008, keyCode=VOLUME_UP(24), scanCode=115, metaState=0x00000000, repeatCount=0), policyFlags=0x62000000, age=1195ms
Change-Id: Ifeb70526c589508220cade800bd104344dc312ab