In particular: consistent rounding and extreme values.
Before, rounding was something like 'away from 0.999...', which led to
surprising corner cases in which the value was rounded up.
Now, rounding is always 'down'.
This even works for 0xffffffff, and also for 0xffffffffffffffffULL on 64-bit.
Windows uses "KB", "MB", "GB" as powers of two.
macOS uses "kB", "MB", "GB" as powers of ten.
"k", "M", "G" are standard SI prefixes that normally refer to powers of
ten.
The IEC introduced "KiB", "MiB", "GiB" to unambiguously refer to
powers of two. It admittedly hasn't caught on that much, but it
does have the advantage that it's unabigious what it means.
So let's use it for user-visible sizes in SerenityOS.
(Linux does all of the above in different places, depending on app and
toolkit.)
Let's use the one in AK/NumberFormat.h everywhere.
It has slightly different behavior than some of the copies this
removes, but it's probably nice to have uniform human readable
size outputs across the system.
The SI prefixes "k", "M", "G" mean "10^3", "10^6", "10^9".
The IEC prefixes "Ki", "Mi", "Gi" mean "2^10", "2^20", "2^30".
Let's use the correct name, at least in code.
Only changes the name of the constants, no other behavior change.
