rewrite at::vec::*::convert_to_int_of_same_size (#98429)
This was failing to compile with unrelated changes in the
windows-binary-libtorch-release build job. This rewrite seems to avoid
that problem.
For an example failure, see:
https://hud.pytorch.org/pytorch/pytorch/commit/144d5268a1ee55a348c36bb6f02b881cc67d5173
Differential Revision: [D44717809](https://our.internmc.facebook.com/intern/diff/D44717809/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98429
Approved by: https://github.com/huydhn
