Make some types and methods related to Polonius + Miri public

[willcrichton]

We have a tool, Aquascope, which uses Polonius and Miri to visualize the compile-time and run-time semantics of a Rust program. Changes in the last few months to both APIs have hidden away details we depend upon. This PR re-exposes some of those details, specifically:

Polonius:

• BorrowSet and BorrowData are added to rustc_borrowck::consumers, and their fields are made pub instead of pub(crate). We need this to interpret the BorrowIndexes generated by Polonius.
• BorrowSet::build is now pub. We need this because the borrowck API doesn't provide access to the BorrowSet constructed during checking.
• PoloniusRegionVid is added to rustc_borrowck::consumers. We need this because it's also contained in the Polonius facts.

Miri:

• InterpCx::local_to_op is now a special case of local_at_frame_to_op, which allows querying locals in any frame. We need this because we walk the whole stack at each step to collect the state of memory.
• InterpCx::layout_of_local is now pub. We need this because we need to know the layout of every local at each step.

If these changes go against some design goal for keeping certain types private, please let me know so we can hash out a better solution. Additionally, if there's a better way to document that it's important that certain types stay public, also let me know. For example, BorrowSet was previously public but was hidden in 6676cec, breaking our build.

cc @RalfJung @nnethercote @gavinleroy

[rustbot]

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[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @rust-lang/wg-const-eval

[rustbot]

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @rust-lang/wg-const-eval

[RalfJung]

This calls after_local_read which has no way of knowing that the local is from a different frame... so things might go wrong in Miri here.

Please extend after_local_read to also receive the &Frame.

[willcrichton]

Done.

[RalfJung]

Do you really need read and write access to all these fields?

If read access suffices, maybe add public getters instead?

[willcrichton]

I don't need write access. I restored the pub(crate) visibility and added getters for BorrowSet and BorrowData.

[lqd]

Additionally, if there's a better way to document that it's important that certain types stay public, also let me know. For example, BorrowSet was previously public

Adding a comment to each def site of interest will help: the fact that they are public is not enough, neither is the fact that they're referenced from consumers. AFAICT this code is has no stability guarantee, so things can (and will) still break but a comment explaining why things are public can help lower the chances of accidental breakage. This is already done in multiple places.

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri