AK: Use IEC prefixes in human_readable_format

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.)

AK/NumberFormat.h

@@ -41,12 +41,12 @@ static String number_string_with_one_decimal(float number, const char* suffix)
 static String human_readable_size(size_t size)
 {
     if (size < 1 * KiB)
-        return String::format("%zu bytes", size);
+        return String::format("%zu B", size);
     if (size < 1 * MiB)
-        return number_string_with_one_decimal((float)size / (float)KiB, "KB");
+        return number_string_with_one_decimal((float)size / (float)KiB, "KiB");
     if (size < 1 * GiB)
-        return number_string_with_one_decimal((float)size / (float)MiB, "MB");
-    return number_string_with_one_decimal((float)size / (float)GiB, "GB");
+        return number_string_with_one_decimal((float)size / (float)MiB, "MiB");
+    return number_string_with_one_decimal((float)size / (float)GiB, "GiB");
 }
 
 }