[sledge] Improve formatting and print indices of witness traces
[sledge] Improve formatting and print indices of witness traces

Summary:
Tweak the output formatting of witness traces to improve readability and
understandability.

Move block indices to the front so that they're not obscured by the long function
names that arise in LLVM in practice (from C++ mangling etc.), and number the
elements of the witness traces for cross-reference.

Differential Revision: D39731568

fbshipit-source-id: d5491ab7ec45a7bbe566ea607c806c2b07c4c08d

facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer