```js
// here, `a?.b.c` is a single optional chain
// (evaluates to undefined if a is nullish)
a?.b.c;
// here, 'a?.b` is an optional chain, and `.c` is an unconditional load
// (nullthrows if a is nullish)
(a?.b).c;
```
---
Next PR in stack will add a bailout for `(a?.b).c`.
(If we want to properly handle `(a?.b).c`, we might want to model optional
chains explicitly in the HIR. We currently assume that any `PropertyLoad` whose
lhs is an optional property load is read conditionally.)