values within initializer blocks.
The issue occurs in code like this:
```
class C {
var b = true
init {
b = false // Missing PUTFIELD for this statement
}
}
```
Added a new statement origin for field initialization (at declaration)
instead of relying on `origin == null` in ExpressionCodegen to determine
whether to generate the initializations.
This was unintentionally broken in
d68a1898d0.
