FR: Caps Lock signal handling

[mayurankv]

I would love a way for the caps lock led state to be modified in Kanata. I'm not familiar with rust or C++ so I wasn't able to fully understand the code but I was wondering if there was a way to send an event like:

• event::type::caps_lock_state_changed (on) is sent via krbn::event_queue::utility::make_queue in karabiner_grabber

Thanks for any help!

P.S. This is from the following example in the Karabiner documents:

### The flow of handling caps lock as modifier

Example:

```json
{
    "from": {
        "key_code": "down_arrow",
        "modifiers": {
            "mandatory": ["caps_lock"],
            "optional": ["any"]
        }
    },
    "to": [
        {
            "key_code": "d"
        }
    ],
    "type": "basic"
}
```

-   Press the physical caps_lock key (`hid::usage::keyboard_or_keypad::keyboard_caps_lock`)
    -   `key_event_dispatcher` is updated.
        -   `pressed_keys_.insert(caps_lock)`
    -   macOS update the caps lock LED state (on).
    -   `event::type::caps_lock_state_changed (on)` is sent via `krbn::event_queue::utility::make_queue` in `karabiner_grabber`.
        -   `modifier_flag_manager increase_led_lock (caps_lock)`
        -   `key_event_dispatcher` is updated.
            -   `pressed_modifier_flags_.insert(caps_lock)`
-   Release the physical caps_lock key (`hid::usage::keyboard_or_keypad::keyboard_caps_lock`)
    -   `key_event_dispatcher` is updated.
        -   `pressed_keys_.erase(caps_lock)`
-   Press `down_arrow` key.j
    -   `sticky_modifier caps_lock false` is sent by `modifiers.mandatory`.
        -   `modifier_flag_manager decrease_sticky (caps_lock)`
    -   `hid::usage::keyboard_or_keypad::keyboard_caps_lock` is sent via virtual hid keyboard.
    -   `key_event_dispatcher` is updated.
        -   `pressed_modifier_flags_.erase(caps_lock)`
    -   `d` is sent via virtual hid keyboard.
    -   sticky_modifiers are erased.
    -   `sticky_modifier caps_lock true` is sent by `modifiers.mandatory`.
        -   `modifier_flag_manager increase_sticky (caps_lock)`
    -   macOS update the caps lock LED state (off).
    -   `event::type::caps_lock_state_changed (off)` is sent via `krbn::event_queue::utility::make_queue` in `karabiner_grabber`.
        -   `modifier_flag_manager decrease_led_lock (caps_lock)`
            -   Note: led_lock will be ignored while other counter is active in modifier_flag_manager.
-   Release `down_arrow` key.
    -   `d` is sent via virtual hid keyboard.
-   Press `tab` key.
    -   `hid::usage::keyboard_or_keypad::keyboard_caps_lock` is sent via virtual hid keyboard by sticky_modifier.
    -   sticky_modifiers are erased.
    -   `tab` is sent via virtual hid keyboard.