The comment previously implied that the true branch would result in the false
block. Fortunately the implementation is correct.

Sometimes a simple goto misses the cleanup/unwind edges. Specifically, in the
case of infinite loops such as those introduced by a loop statement without any
other out edges. Analogous to TerminatorKind::FalseEdges; this new terminator
kind is used when we want borrowck to consider an unwind path, but real control
flow should never actually take it.

Fixes rust-lang#46036

Fix instructions on existing mir-opt tests after introducing false edges from
loops. Also, add a test for issue 46036: infinite loops.

As opposed to using weirdness involving pretending the body block
is the loop block. This does not pass tests

This commit is [ci skip] because I know it doesn't pass tests yet.
Somehow this commit introduces nondeterminism into the handling of
loops.

Fixes the hash test to recognize that MirValidated can change when changing
around labels, and add a new test that makes sure we're lowering loop statements
correctly.