Add Windows app icon resource & load it

Add Windows resource files and load the app icon in the window class. Introduce resources/nebula.rc and resources/resource.h (defines IDI_APPICON referencing assets/images/branding/Nebula-Favicon.ico). Include resource.h in nebula_window_win.cpp and set window_class.hIcon/hIconSm via LoadImageW. Update CMakeLists.txt to compile the .rc and add the resources include directory for Windows.

CMakeLists.txt

@@ -60,6 +60,7 @@ if(OS_WINDOWS)
         src/platform/win/startup_win.cpp
         src/platform/win/browser_host_win.cpp
         src/platform/win/nebula_window_win.cpp
+        resources/nebula.rc
     )
 elseif(OS_MACOSX)
     set(NEBULA_PLATFORM_SOURCES
@@ -156,6 +157,9 @@ function(add_nebula_app_target nebula_target entry_source)
 
     if(OS_WINDOWS)
         target_link_libraries(${nebula_target} PRIVATE dwmapi)
+        target_include_directories(${nebula_target} PRIVATE
+            "${CMAKE_SOURCE_DIR}/resources"
+        )
         target_compile_definitions(${nebula_target} PRIVATE
             NOMINMAX
             WIN32_LEAN_AND_MEAN