[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/box/objects/initializerBlockResetToDefault.kt

@@ -0,0 +1,33 @@
+object C {
+  var myIntProp: Int = 1
+  var myByteProp: Byte = 2
+  var myLongProp: Long = 3L
+  var myShortProp: Short = 4
+  var myDoubleProp: Double = 5.6
+  var myFloatProp: Float = 7.8f
+  var myBooleanProp: Boolean = true
+  var myCharProp: Char = '9'
+
+  init {
+    myIntProp = 0
+    myByteProp = 0
+    myLongProp = 0L
+    myShortProp = 0
+    myDoubleProp = 0.0
+    myFloatProp = 0.0f
+    myBooleanProp = false
+    myCharProp = '\u0000'
+  }
+}
+
+fun box(): String {
+  if (C.myIntProp != 0) return "fail Int"
+  if (C.myByteProp != 0.toByte()) return "fail Byte"
+  if (C.myLongProp != 0L) return "fail Long"
+  if (C.myShortProp != 0.toShort()) return "fail Short"
+  if (C.myDoubleProp != 0.0) return "fail Double"
+  if (C.myFloatProp != 0.0f) return "fail Float"
+  if (C.myBooleanProp != false) return "fail Boolean"
+  if (C.myCharProp != '\u0000') return "fail Char"
+  return "OK"
+}