[syntax_tools] Introduce Unicode support for Erlang source files

Not complete.
Unicode in wild attribute doesn't work.
No support for Unicode regarding Igor stubs.
syntax_tools: Remove support for packages
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.
Remove support for the query keyword and query expressions
Merge branch 'nox/enable-silent-rules/OTP-10726'

* nox/enable-silent-rules/OTP-10726:
  Implement ./otp_build configure --enable-silent-rules
Merge branch 'lh/forget-mnemosyne/OTP-10729'

* lh/forget-mnemosyne/OTP-10729:
  Remove what remains of the Mnemosyne code
  Remove support for the query keyword and query expressions
Turn warnings to errors on selected applications
Extend char() to Unicode characters

The code related to the introduction of unicode_string() and
unicode_char() has been removed. The types char() and string() have
been extended to include Unicode characters.

In fact char() was changed some time ago; this commit is about
cleaning up the documentation and introduce better names for some
functions.
Prepare release