These changes are compatible with clang-format 16 and will be mandatory
when we eventually bump clang-format version. So, since there are no
real downsides, let's commit them now.
This allows us to get rid of an include to LibC/sys/ttydefaults.h in the
Kernel TTY implementation.
Also, move ttydefchars static const struct to another file called
Kernel/API/ttydefaultschars.h, so it could be used too in the Kernel TTY
implementation without the need to include anything from LibC.