Use /utf-8 with MSVC build

/utf-8 is equivalent to /source-charset:utf-8 /execution-charset:utf-8.

Now that all source files (except for included third-party headers
outside of this repository) are in UTF-8, we must set source-charset to
utf-8, because otherwise the default (on our build machines) is CP-1252.
(The compiler does not auto-detect UTF-8 source files unless they have a
UTF-8 BOM, which we do not use.)

The execution charset determines how (non-wide) string literals are
encoded in the executable binary. UTF-8 is usully appropriate for our
string constants (such as property names and values), because JNI and
SWIG assume UTF-8 and C/C++ library functions work with UTF-8.

Our only examples of non-ASCII characters in string literals (at least
among the files recently converted to UTF-8) are 8-bit characters from
iso-8859-1 (latin1) (there are one or two exceptions that are
insignificant). These, if exposed to the CMMCore API (to Java or Python)
were presumably working just because UTF-8 is a superset of iso-8859-1
(but not of CP-1252) -- they were stored in the binary as CP-1252 but
treated by SWIG-generated code as UTF-8.

(Use of non-ASCII characters in property names and other such strings is
still not a very good idea, but we don't want to change names that will
invalidate configuration files.)

As far as I can tell, the conversion of source code to UTF-8 and the
introduction of /utf-8 do not interact with the project Character Set
setting (Unicode or Multi-byte), which only control whether the Win32
API functions default to the "A" or "W" version.

Incidentally, use of /utf-8 also helps to prepare for the switch to
Meson, which adds /utf-8 by default.

buildscripts/VisualStudio/MMCommon.props

@@ -27,6 +27,7 @@
       <ExceptionHandling>Sync</ExceptionHandling>
       <PreprocessorDefinitions>_CRT_SECURE_NO_WARNINGS;_SCL_SECURE_NO_WARNINGS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <MultiProcessorCompilation>true</MultiProcessorCompilation>
+      <AdditionalOptions>/utf-8 %(AdditionalOptions)</AdditionalOptions>
     </ClCompile>
     <Link>
       <GenerateDebugInformation>true</GenerateDebugInformation>