Cross Crate Analysis 2: An alternative approach.

[JustusAdam]

What Changed?

Adds the capability to load bodies and borrowcheck facts from non-local crates to facilitate analysis across the boundaries of the local crate. The design of this implementation is based on a similar mechanism in a purity analyzer by @artemagvanian.

Adds the --include command line argument to specify names of crates that should be loadable in addition to the analysis target.

The basic mechanism is that, in every selected crate (either main target or --include) we run a visitor after expansion that uses get_body_with_borrowck_facts, sanitizes that body by removing crate-local data and writes it plus relevant lifetime information to disk using Encodable. Downstream crates can locate the written data and load it back in using Decodable. A nicety of this approach is that we always do this, even or the main target crate, which means there is only one code path instead of a separate local and remote one.

I the process of implementing this I realize that our points-to analysis actually doesn't need the whole BodyWithBorrockFacts but only input_facts.subset_base (and the body itself). I parameterized the points-to analysis, such that it can accept a reduced input, and we only store the relevant data.

Also fully supports marker annotations in foreign crates.

The implicit body cache MIR_BODIES we used before is now replaced by an explicit BodyCache.

A large part of the changes is just changing LocalDefId to DefId in call strings and the like as well as ensuring that all places that used to call rustc_utils' get_body_with_borrowck_facts is replaced with loading from the BodyCache.

Caveats

The statistics about how many functions were seen etc are disabled for now (always 0).

Why Does It Need To?

Analyzing only the local crate is a severe limitation of the tool which would be lifted by this PR.

There is a concurrent attempt (#153) to address the same issue. This is a simpler, but potentially less scalable approach. In addition this approach has full support for "both directions" of cross crate. The "forward direction" extends the PDG from the local crate (main analysis target) such that it also models functions in dependencies. The "backwards" direction ensures that function in the dependency, which are parameterized by traits where the impl is in the local trait, that impl composes with the function in the dependency.

Checklist

• Above description has been filled out so that upon quash merge we have a
  good record of what changed.
• New functions, methods, types are documented. Old documentation is updated
  if necessary
• Documentation in Notion has been updated
• Tests for new behaviors are provided
  • New test suites (if any) ave been added to the CI tests (in
    .github/workflows/rust.yml) either as compiler test or integration test.
    Or justification for their omission from CI has been provided in this PR
    description.