Differ this/non-this instances for vars initialization in class

When deal with constructed object (not this) treat it like it's fully initialized.

Otherwise (this or access with no receiver) access instruction
should be handled as it was before.

 #KT-6788 Fixed
 #KT-4126 Fixed

compiler/testData/diagnostics/tests/controlFlowAnalysis/kt4126.kt

@@ -0,0 +1,3 @@
+public data class ProductGroup(val short_name: String, val parent: ProductGroup?) {
+    val name: String = if (parent == null) short_name else "${<!DEBUG_INFO_SMARTCAST!>parent<!>.name} $short_name"
+}