The underflow reports of checker security.ArrayBound previously
displayed the (negative) byte offset of the accessed location; but those
numbers were a bit hard to decipher (especially when the elements were
large structs), so this commit replaces the byte offset with an index
value (if the offset is an integer multiple of the size of the accessed
element).
This change only affects the content of the messages; the checker will
find the same issues before and after this commit.
This commit finishes the reorganization of the tests for the checker
`security.ArrayBound`.
Previously these tests were all named `out-of-bounds-*` which was only
weakly connected to the checker name; this commit moves them to a
directory named after the checker (`ArrayBound`). I decided to use a
directory instead of the more common filename prefix ("poor man's
directory") system because it seems to be a more natural use of the
filesystem and there are already a few precedents for it.
I also added (or edited) comments at the beginning of each test file to
describe their purpose; and I added a single new testcase to highlight
that the assumption note tags can be added to reports by any checker.
(Previously all tests in the file triggered out-of-bounds reports to
reveal the note tags; but that was just for convenience.)
