Add support for loop-contract historic values

[thanhnguyen-aws]

Add support for old and prev to refers to historic values in loop contracts where

• old(expr) refers to the value of the expr before the loop.
• prev(expr) refers to the value of the expr at the previous iteration.

Resolves #3697

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[tautschnig]

Looks like you want to run kani-fmt.sh to address the test failure.

[qinheping]

Could you add some comments to explain when should_replace return true?

[qinheping]

Could you add more comments to the newly added functions?

[remi-delmas-3000]

Could we use on_entry(...) instead of old(...) ? The doc itself says "old(...) denotes the value on loop entry".

Some documentation describing the transformation at a high level would help the review.

[carolynzech]

You should remove details that will be brittle between runs (like the check number, or the .1). We also don't typically include location. You should have backslashes between the lines to enforce that the lines are consecutive--with this writing, something like this would pass:

loop_with_old.loop_invariant_base.1
	 - Status: FAILURE

random_other_check
     - Status: SUCCESS

Without the backslashes, it'll just check for each line in isolation, so there's nothing tying the success to the particular property we care about.

I'd recommend looking at other expected files for examples.