Prepare OTP files for Unicode as default encoding
Implement ./otp_build configure --enable-silent-rules

With silent rules, the output of make is less verbose and compilation
warnings are easier to spot. Silent rules are disabled by default and
can be disabled or enabled at will by make V=0 and make V=1.
Merge branch 'nox/enable-silent-rules/OTP-10726'

* nox/enable-silent-rules/OTP-10726:
  Implement ./otp_build configure --enable-silent-rules
Prepare release
Update copyright years
Use erlang:demonitor(Ref, [flush]) where applicable
Rename and document lists:zf/2 as lists:filtermap/2

This function is used all over the place in OTP itself and people
sometimes want that functionality, they may as well not reimplement it
themselves.
versions updates for erl_interface, et and os_mon