use a newtype for the variant discriminant in trans instead of u64

[oli-obk]

This is groundwork for #30587 (typestrong constant integrals), but imo it's a change that in itself is good, too, since we don't just juggle u64s around anymore.

ty::Disr will be changed to a ConstInt in #30587

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @arielb1 (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[bors]

☔ The latest upstream changes (presumably #30890) made this pull request unmergeable. Please resolve the merge conflicts.

[oli-obk]

rebased

[pnkfelix]

at least some of the travis failure error messages seems related to this PR?

[oli-obk]

sorry about that. This time make check-stage1 ran through fine

[arielb1]

@bors r+

[bors]

📌 Commit 6fef118 has been approved by arielb1

[bors]

⌛ Testing commit 6fef118 with merge 0b524ed...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt