Instrument validity checks for pointer to reference casts for slices and str's

[zhassan-aws]

As pointed out in #3498, validity checks for pointer to reference casts (added in #3221) were not instrumented in the case of fat pointers (e.g. array and string slices). This PR extends the instrumentation of validity checks to handle those cases.

Resolves #3498

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

[celinval]

I pushed a fix for the test, but as I mentioned before. I think we could create a new test from the existing one that shows the new code catch those issues.

BTW, I think the code we added still does not check alignment.

[zhassan-aws]

I think we could create a new test from the existing one that shows the new code catch those issues.

Added as an expected test.

[celinval]

Thanks!