[Operator Versioning][Edge] Reorganize upgrader initialization logic for thread safety (#70225)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70225
Thanks for zhxchen17's suggestion. This pr move the operator initialization logic to `upgrader_mobile.cpp`, such that we can leverage the static variable to ensure the operator initialization only happens once.
ghstack-source-id: 146103229
Test Plan:
```
buck test mode/opt //papaya/integration/service/test/analytics/histogram:generic_histogram_system_test -- --exact 'papaya/integration/service/test/analytics/histogram:generic_histogram_system_test - SumHistogramSystemTest.test' --run-disabled
buck test mode/opt //caffe2/test/cpp/jit:jit
buck test mode/dev //papaya/integration/service/test/mnist:mnist_system_test -- --exact 'papaya/integration/service/test/mnist:mnist_system_test - MnistFederatedSystemTest.test'
```
Reviewed By: zhxchen17
Differential Revision: D33247543
fbshipit-source-id: 6c3a87fe909a1be01452fa79649065845b26d805
