[clang][dataflow] Add option for simpler boolean model

Currently the CDF boolean model involves SAT queries, which are handled by the WatchedLiteralsSolver (or could also be handled with Z3 or in custom builds any other solver -- see issue #204593).

An old prototype https://github.com/llvm/llvm-project/pull/82950 adds an alternative boolean model that didn't require SAT queries. We could try to brush that up and make it a runtime/checker option.

Pros:
- fewer dependencies
- could be faster (need to benchmark)

Cons:
- the `allows` or `proves` queries are more conservative and wouldn't handle correlated branches (https://clang.llvm.org/extra/clang-tidy/checks/bugprone/unchecked-optional-access.html#ensure-that-a-value-exists-then-access-the-value-in-a-correlated-branch)

Start by reviewing the current CDF boolean model and WatchedLiteralsSolver, then compare the alternative implementation in pull request #82950. Define how a runtime or checker option should select the model, benchmark both approaches, and verify the documented conservative behavior around correlated branches.

Written by the indexing model from the issue text.