Reduce build time for op_where by consolidating bool & byte (#3416)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3416

bool is implicitly convertible to uint8_t, so I think this should Just Work?

Reviewed By: manuelcandales

Differential Revision: D56650339

fbshipit-source-id: 05c4db9c6f661f992f511611611a2e8767b260a8