[analyzer] Update Open Projects and Potential Checkers pages.

- va_list checker (PR16811 and PR16812)
- Model floating-point values
- Bound bitwise masking operations (PR16615)
- Bound C string length (PR16558 and others)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188127 91177308-0d34-0410-b5e6-96231b3b80d8