[clang] [NFC][analyzer] Eliminate NodeBuilder from ExprEngine visit methods and from their utility methods (PR #212186)

[Donát Nagy via cfe-commits]

================
@@ -451,7 +444,8 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
           if (T->isReferenceType()) {
             // A bad_cast exception is thrown if input value is a reference.
             // Currently, we model this, by generating a sink.
-            Bldr.generateSink(CastE, Pred, state);
+            Dst.insert(Engine.makePostStmtNode(CastE, state, Pred,
+                                               /* MarkAsSink */ true));
----------------
NagyDonat wrote:

```suggestion
            Engine.makePostStmtNode(CastE, state, Pred, /*MarkAsSink=*/true);
```
`ExplodedNodeSet` has an invariant that it never contains [null or] sink nodes, trying to insert a sink node is a no-op (and `MarkAsSink` guarantees that the result is null or sink).

The only effect of creating a sink node is that:
- it will appear in the exploded graph as a child of its parent node;
- it can be used as an error node in a checker that wants to create a bug report.

Note that we often use the phrase "we sink the execution path" but the sink node itself is usually irrelevant and the "real" effect of `generateSink` is that it removes the parent of the sink node from the `Frontier` of the node builder (without inserting a new node into the `Frontier`).

After the removal of the `NodeBuilders` it becomes easier to see that these sinks are mostly useless (although their presence in the graph can influence a few things) -- but the were already mostly useless even before the refactoring.

https://github.com/llvm/llvm-project/pull/212186