Rollup merge of #116589 - Zalathar:successors, r=oli-obk

coverage: Unbox and simplify `bcb_filtered_successors`

This is a small cleanup in the coverage instrumentor's graph-building code.

---
This function already has access to the MIR body, so instead of taking a reference to a terminator, it's simpler and easier to pass in a basic block index.

There is no need to box the returned iterator if we instead add appropriate lifetime captures, and make `short_circuit_preorder` generic over the type of iterator it expects.

We can also greatly simplify the function's implementation by observing that the only difference between its two cases is whether we take all of a BB's successors, or just the first one.

---

`@rustbot` label +A-code-coverage

0 files changed, 0 insertions, 0 deletions