[JVM IR] Fix issue where fields are not being set to their default

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.

compiler/testData/codegen/bytecodeText/redundantValInitializer.kt

@@ -90,5 +90,8 @@ class NonRedundantInitializers {
     val myFloat: Float = -0.0f
 }
 
+// There is 1 PUTSTATIC for the companion object instance.
+
 // 0 PUTFIELD RedundantInitializersToDefault
 // 2 PUTFIELD NonRedundantInitializers
+// 1 PUTSTATIC