[clang] [analyzer] Add optin.taint.TaintedDiv checker (PR #106389)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat commented:

Looks good overall, I added several suggestions but they mostly tweak the documentation and the comments.

Moreover, I don't see any tests where the separation between  `optin.taint.TaintedDiv` and `core.DivideZero` is tested by enabling one of them and disabling the other. You should probably add a new short test file for this where:
 - taint modeling is active;
 - there are two RUN lines (with different `-verify=...` tags): one that enables `optin.taint.TaintedDiv` and one that enables `core.DivideZero`;
 - there are testcases that perform division by:
   - a value that comes from a tainted source and is known to be zero at the point of division (I know that e.g. in an `if (x == 0)` block `getSVal()` will return a `ConcreteInt` as the value of `x` instead of the (potentially tainted) symbol that was used to represent it earlier -- but it would be still nice to see this situation.)
   - a value that comes from a tainted source and may be either zero or nonzero;
   - a value that comes from a tainted source and is known to be nonzero.

https://github.com/llvm/llvm-project/pull/106389