There is major a bug found in iterator modeling: upon adding a value
to or subtracting a value from an iterator the position of the original
iterator is also changed beside the result. This patch fixes this bug.
To catch such bugs in the future we also changed the tests to look for
regular expressions including an end-of-line symbol (`$`) so we can
prevent false matches where only the tested prefix matches.
Another minor bug is that when printing the state, all the iterator
positions are printed in a single line. This patch also fixes this.
Differential Revision: https://reviews.llvm.org/D82385
ea563daae5