This change has many improvements:
- We don't use `LockRefPtr` to hold instances of many base devices as
with the DeviceManagement class. Instead, we have a saner pattern of
holding them in a `NonnullRefPtr<T> const`, in a small-text footprint
class definition in the `Device.cpp` file.
- The awkwardness of using `::the()` each time we need to get references
to mostly-static objects (like the Event queue) in runtime is now gone
in the migration to using the `Device` class.
- Acquiring a device feel more obvious because we use now the Device
class for this method. The method name is improved as well.
The following changes take effect:
1. Annotate FixedStringBuffer => `FixedStringBuffer` in many places.
2. Remove non-existing helpers for FixedStringBuffers. I added them
previously but even then they were removed in a following fixup so these
references were never valid. Therefore let's just put a vague reference
to the fact that we have some helpers for this class in the Kernel, and
let people to figure out quickly by themselves for this topic.
3. Put a sentence to explain that FixedStringBuffer objects are not only
being used in syscall handling code, but also for storing actual data in
both the Thread and Process classes as well.
