Kernel: Allow remapping Caps Lock to Control (#6883)

We use a global setting to determine if Caps Lock should be remapped to
Control because we don't care how keyboard events come in, just that they
should be massaged into different scan codes.

The `proc` filesystem is able to manipulate this global variable using
the `sysctl` utility like so:

```
# sysctl caps_lock_to_ctrl=1
```

Kernel/Devices/HID/KeyboardDevice.h

@@ -53,6 +53,7 @@ protected:
     virtual const char* class_name() const override { return "KeyboardDevice"; }
 
     u8 m_modifiers { 0 };
+    bool m_caps_lock_to_ctrl_pressed { false };
     bool m_caps_lock_on { false };
     bool m_num_lock_on { false };
     bool m_has_e0_prefix { false };