Auto merge of #33667 - pnkfelix:fixes-to-mir-dataflow, r=arielb1

Fixes to mir dataflow

Fixes to mir dataflow

This collects a bunch of changes to `rustc_borrowck::borrowck::dataflow` (which others have pointed out should probably migrate to some crate that isn't tied to the borrow-checker -- but I have not attempted that here, especially since there are competing approaches to dataflow that we should also evaluate).

These changes:
 1. Provide a family of related analyses: MovingOutStatements (which is what the old AST-based dataflo computed), as well as MaybeInitialized, MaybeUninitalized, and DefinitelyInitialized.
   * (The last two are actually inverses of each other; we should pick one and drop the other.)
 2. Fix bugs in the pre-existing analysis implementation, which was untested and thus some obvious bugs went unnoticed, which brings us to the third point:
 3. Add a unit test infrastructure for the MIR dataflow analysis.
   * The tests work by adding a new intrinsic that is able to query the analysis state for a particular expression (technically, a particular L-value).
   * See the examples in compile-fail/mir-dataflow/inits-1.rs and compile-fail/mir-dataflow/uninits-1.rs
   * These tests are only checking the results for MaybeInitialized, MaybeUninitalized, and DefinitelyInitialized; I am not sure if it will be feasible to generalize this testing strategy to the MovingOutStatements dataflow operator.

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