rename plugin from PolyvoxFilament to FlutterFilament

rename plugin from PolyvoxFilament to FlutterFilament

windows/opengl_texture_buffer.cpp

@@ -7,7 +7,7 @@
 
 #include <thread>
 
-namespace polyvox_filament {
+namespace flutter_filament {
 
 void _release_callback(void *releaseContext) {
   // ((OpenGLTextureBuffer*)releaseContext)->unlock();
@@ -137,4 +137,4 @@ OpenGLTextureBuffer::~OpenGLTextureBuffer() {
     wglMakeCurrent(NULL, NULL);
 }
 
-} // namespace polyvox_filament
+} // namespace flutter_filament