CFA merge for definition / initialization : more accurate handling of unknown variables #KT-13969 Fixed

(cherry picked from commit 4a96589)

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

@@ -0,0 +1,6 @@
+fun test(cond1: Boolean) {
+    do {
+        if (cond1) continue
+        val cond2 = false
+    } while (<!UNINITIALIZED_VARIABLE!>cond2<!>) // cond2 may be not defined here
+}