chore: internalize flow-router (from meteor 3 branch) (#31365)

apps/meteor/packages/flow-router/.gitignore

apps/meteor/packages/flow-router/.npm/package/.gitignore

apps/meteor/packages/flow-router/.npm/package/README

...eor/packages/flow-router/.npm/package/npm-shrinkwrap.json

apps/meteor/packages/flow-router/client/_init.js

apps/meteor/packages/flow-router/client/group.js

apps/meteor/packages/flow-router/client/modules.js

apps/meteor/packages/flow-router/client/route.js

apps/meteor/packages/flow-router/client/router.js

apps/meteor/packages/flow-router/client/triggers.js

apps/meteor/packages/flow-router/lib/router.js

apps/meteor/packages/flow-router/package.js

apps/meteor/packages/flow-router/server/_init.js

apps/meteor/packages/flow-router/server/group.js

...meteor/packages/flow-router/server/plugins/fast_render.js

apps/meteor/packages/flow-router/server/route.js

apps/meteor/packages/flow-router/server/router.js