Untrack auto generated files under windows/flutter/. Add below files into .gitignore

windows/flutter/generated_plugin_registrant.cc
windows/flutter/generated_plugin_registrant.h
windows/flutter/generated_plugins.cmake

.gitignore

@@ -12,4 +12,4 @@ Cargo.lock
 **/*.db
 .idea/
 /flowy-test/
-.ruby-version
+.ruby-version

frontend/app_flowy/.gitignore

@@ -55,4 +55,7 @@ windows/flutter/dart_ffi/
 **/**/*.a
 **/**/*.lib
 **/**/*.dll
-**/**/*.so
+**/**/*.so
+flutter/generated_plugin_registrant.cc
+flutter/generated_plugin_registrant.h
+flutter/generated_plugins.cmake