[ty] Infer empty collection constructors from later uses (#26389)
## Summary
Unannotated collection literals participate in full-scope bidirectional
inference, but empty constructor calls (`list()`, `set()`, and `dict()`)
did not. For example, we previously accepted this function because
`result` remained `set[Unknown]`:
```python
def make_set() -> set[str]:
result = set()
result.add(1)
reveal_type(result) # revealed: set[int | str]
return result # error: [invalid-return-type]
```
This PR treats bare, zero-argument `list()`, `set()`, and `dict()`
assignment values as collection initializers in the semantic index and
reuses the existing collection-use constraint inference. (For now, we
don't support aliased or attribute-accessed calls.)
Closes https://github.com/astral-sh/ty/issues/3573.
