As this changes the precision on static-buffer-overflow query, please do not merge before GHES 3.3 has been branched.

This PR includes:

• Further relax predicate memberMaybeVarsized to include all members of size 0 or 1
• Remove warnings for static buffer overflows in when fields are indexed as an argument to offsetof
• Do not warn on static buffer overflows if upper bound analysis used widening.
• Weaken wording on overflow static alert text (is accessed -> may be accessed)

Statistics from running OverflowStatic on all LGTM projects:

[*] Unknown alerts denotes alerts, where I cannot judge if the alerts is correct. These usually includes nested macro expansions.

The false positives can be grouped into:

• Copying multiple fields (7 FP's)
• Limitations in the range analysis (1 FP)
  • 1 reasonably trivial
  • 3 are non trivial, and would require a deeper invariant analysis.
• Dead code (2 FP's)
• Wrong assumption of page_size (evaluated to 0) (1 FP)
• Variable sized member of size 4 (char data[sizeof(int)]) (2 FP)

Detailed results and the actual analysis can be found here:
https://gist.github.com/andersfugmann/5091e7c63cd4f6ae94d3b86e426efd77