[observer] Fix crashdump_viewer tests for R16

Generate dumps for r14, r15 and r16.
Save generated dumps if test fails.
[observer] Set ERL_CRASH_DUMP_SECONDS/=-1 on old releases

Else, crashdumps can not be generated.
Prepare OTP files for Unicode as default encoding
observer: Fix font sizes

On wxWidgets 2.9 they seem to have fixed font sizes in GC's
Observer: Fix distribution dialog
observer: Fix check for graphics contexts

wxWidgets-2.9 seg faults if you try to create a graphics context
before the window is shown.

With bad timing this can happen.

So change the haveGC test to check if the functionality is available
without creating the GraphicsContext.
wx: Workaround wx-2.9 bugs

Menuhandling in 2.9 is (currently) buggy on mac,
this avoids a crash in menu handling but causes a lot unusable menus.
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
Turn warnings to errors on selected applications
Update copyright years
Prepare release