[FIR] Complete data-flow analysis for all control-flow graph nodes

There are conditions where the data-flow analysis for a control-flow
graph node is delayed. Make sure that when completing a graph, all nodes
within the graph have completed their data-flow analysis.

^KT-61794 Fixed

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

@@ -0,0 +1,9 @@
+// FIR_IDENTICAL
+// ISSUE: KT-61794
+
+private fun createStubFunction(expression: String?): String? {
+    val tmp = expression?.let {
+        it
+    } ?: return null
+    return tmp
+}