win-wasapi: Fix legacy CMake

Follow-up to 1d5d4b29e7f48f9c414388f900d983f0eeef77df:

win-wasapi: Handle changes to the default monitoring device

Splits the WASAPINotify class out of win-wasapi.cpp and makes it a
shared object in the plugin, then also creates a callback to reset
audio monitoring if the default output device changes.

plugins/win-wasapi/cmake/legacy.cmake

@@ -3,7 +3,8 @@ project(win-wasapi)
 add_library(win-wasapi MODULE)
 add_library(OBS::wasapi ALIAS win-wasapi)
 
-target_sources(win-wasapi PRIVATE win-wasapi.cpp enum-wasapi.cpp enum-wasapi.hpp plugin-main.cpp)
+target_sources(win-wasapi PRIVATE win-wasapi.cpp wasapi-notify.cpp wasapi-notify.hpp enum-wasapi.cpp enum-wasapi.hpp
+                                  plugin-main.cpp)
 
 set(MODULE_DESCRIPTION "OBS WASAPI module")