Provide line numbers for exceptions in object initializer expressions

When using object initializers, like above, all exception stack traces point to the main statement

```
var myObject = new MyClass
{
Property1 = F(),
Property2 = G(),
}
```

This is very suboptimal from an error handling exception, making it so we don't use non-trivial object initializers where I work.

Could this be improved so we get real sequence points between each initialization?

I have seen #5477, which is similar, but relates to anonymous types, so I think this suggestion is slightly different (without knowing the details about lowering, I hope each assignment is its own statement