Adds the public facade on top of the AstNodeImpl adapter from the
previous commit. Re-exposes the same API surface as
semmle/python/Flow.qll (ControlFlowNode, CallNode, BasicBlock,
NameNode, DefinitionNode, CompareNode, ...), backed by the shared
codeql.controlflow.ControlFlowGraph library.
- semmle.python.controlflow.internal.Cfg — public facade.
- ControlFlow/store-load/* — basic store/load coverage via the facade.
The new CFG library is added additively: it has zero callers in lib/
and src/, and the legacy CFG in semmle/python/Flow.qll remains the
default. Dataflow, SSA, and production query migration land in
follow-up PRs.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
