The legacy CFG emitted two ControlFlowNodes for `x[i] += 42` (one load,
one store, with `load.strictlyDominates(store)`). The new CFG collapses
them to a single canonical node, mirroring Java's single-`VarAccess`
model where `isVarRead`/`isVarWrite` are non-disjoint on the same
expression. Reconcile two legacy two-node behaviours with the merged
single-node world:
1. `Cfg::ControlFlowNode.isLoad()` no longer excludes augmented
targets — both `isLoad` and `isStore` hold on the merged canonical
node, matching Java. `NameNode.defines` drops the now-redundant
`not isLoad` guard; `Py::Name.defines` already filters by
`isDefinition` (Store/Param/AugAssign-target ctx).
2. `LocalFlow::definitionFlowStep` is restricted to NameNode targets,
matching legacy ESSA's `assignment_definition` which required
`defn.(NameNode).defines(v)`. Subscript and attribute writes
(`x[i] = 42`, `obj.attr = 42`) no longer emit a local-flow step
*into* the LHS expression — that flow is handled by the AttrWrite
and content-flow machinery. This is essential for keeping augmented
Subscript/Attribute targets classifiable as `LocalSourceNode` on
the read side, which the API graph requires for emitting Use edges.
`StoreLoadTest.ql` is updated to filter `isAugLoad` out of the regular
`load` tag, mirroring the pre-existing `not isAugStore` filter on the
`store` tag so augmented-assignment expectations remain
`augload=n augstore=n` (not also `load=n store=n`).
Closes the three remaining ApiGraphs library-test failures
(`getSubscript.ql` semantically, plus cosmetic toString updates in
`ModuleImportWithDots.ql` and `test_crosstalk.ql`).
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
