Improve compiler error messages of the op registration API (#18550)

Improve compiler error messages of the op registration API (#18550)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18550

When the operator registration API is used wrongly, in most cases we should now get a nice compiler error
instead of weird template error messages.

This is done by making the enable_if conditions more broad so they also match error cases,
but then having static_asserts against these error cases inside the function.
Before that, since the function didn't match, the error message said something like "no function found to match your call",
now it will show the error message specified in the static_asserts.

Reviewed By: dzhulgakov

Differential Revision: D14659178

fbshipit-source-id: 7ca4fb72d9051eadf0a7e2717b962bf1213a52b2