Keep CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS alongside explicit BTCPP_API macros

The BTCPP_API export macro was only applied to a few key classes, but
many free functions and other class members still need to be exported.
Restore CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS as a catch-all while keeping
the explicit export macros for forward compatibility.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: facontidavide

CMakeLists.txt

@@ -216,6 +216,7 @@ if (WIN32)
 endif()
 
 if (BTCPP_SHARED_LIBS)
+    set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
     add_library(${BTCPP_LIBRARY} SHARED ${BT_SOURCE})
     target_compile_definitions(${BTCPP_LIBRARY}
         PUBLIC BTCPP_SHARED_LIBS