When writing using erlang:display* when detached the
write operation would return an error on windows. So
we make sure that the handles are valid so that they
can always be written to.

shell:whereis_evaluator was only used by the pman application
but was not removed when that application was removed.

This makes observer better at drawing the application tree

The protocol replies enotsup for any unkown, so we can
send unknown terms. This is useful when we want to be able
to extend the options allowed to be sent.

Closes erlang#4225

In order to avoid spinning in `user_sup` we start user
during the synchronous phase of `user_drv` startup.

See erlang#4895 for more details

This commit re-implements the entire tty driver for both Unix
and Windows to use a common nif instead of two seperate drivers.

The Unix implementation works pretty much as it did before only that
a lot more of the terminal logic has been moved from Erlang to C.

The windows implementation now uses Windows Terminal Sequences, i.e.
the same sequences as most Unixes to control the terminal. This means
that werl.exe is no longer needed and erl.exe will have the "newshell"
with all the features normally only found on Unix.

The new implementation also uses dirty I/O threads for all I/O which
means that it can leave the FDs in blocking mode. This fixes problems
when the Erlang tty is interacting with other systems such as bash.

Closes erlang#3150
Closes erlang#3390
Closes erlang#4343

We want as much of the I/O work as possible to go through
the user_drv as it will use dirty I/O schedulers to schedule
the work. Also this makes the unicode detection work even
for -noshell/-noinput type systems.

This commit also adds user_drv:start_shell/0 to allow the user
to start the shell after the fact. For instance when rebar3
starts as en escript it may want to start a shell depending on
what arguments are given to it.

This is useful to have when checking if the target of
output is a terminal.

If the cleanup code in sys_tty_reset is never run it can leave
the terminal in a broken state. The cleanup code is not executed
if erts receives a SIGKILL or if Ctrl-C is pressed when +B is started.

Closes erlang#3150

Not clearing it triggered the assert below when stdin
was deselected.

Argument parsing by init is a bit naive. In the escript testcase
"-noshell xxxx...." was interpreted as the "-noshell" flag being
given the value "xxxx....". So to fix this, we push the "-boot file"
argument last and thus "xxxxx" will be seen as a separate argument
as it should.

This is needed for when prim_tty is cover compiled.

When running in embedded mode the on_load function is called
by the init process after the user processes are started. So
we add a way for user to call the on_load function earlier
in the boot sequence so that the shell can be started when
it should.

We cannot move the on_load calls for all modules to an earlier
place in the kernel boot sequence as the code in on_load may
depend on kernel services being started.