[caffe2/utils] Add explicit rule to avoid package boundary violation (#60677)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/60677
Add a rule to wrap conversions.h and depend on that, rather than
relying on a glob which violates package boundaries.
Test Plan: `buck2 build fbcode//caffe2/caffe2:caffe2_core`
Reviewed By: mzlee
Differential Revision: D29370841
fbshipit-source-id: d4dd383eb8457d4f5118574e34e6f17c32fde647
