Add detection of overflow during integer conversion

[findmyhappy]

Summary

G109 provides detection of overflow during strconv.Atoi, but there seems to be no good way to detect the more common conversions between integers, such as uint32 to int32.

Steps to reproduce the behavior

gosec version

Go version (output of 'go version')

Operating system / Environment

Expected behavior

Actual behavior

[ccojocar]

This is a good addition. I was also thinking about a rule to detect this conversions which can lead to overflows.