cmake HAVE_WEBNN examples

SsageParuders/Android_Native_Surface my_android_opencv/cmake/OpenCVDetectWebNN.cmake :42 

message(STATUS "Set HAVE_WEBNN = ${HAVE_WEBNN}")

SsageParuders/Android_Native_Surface my_android_opencv/modules/dnn/CMakeLists.txt :23 

add_definitions(-DHAVE_WEBNN=1)