FIR: Fix builder inference case with independent calls inside lambda

compiler/testData/diagnostics/testsWithStdLib/builderInference/completeIrrelevantCalls.kt

@@ -0,0 +1,16 @@
+// FIR_IDENTICAL
+// SKIP_TXT
+
+class A {
+    lateinit var m: Map<String, Int>
+
+    @ExperimentalStdlibApi
+    fun foo(xs: Collection<List<String>>) {
+        m = buildMap {
+            // flatMap calls might be completed on early phase
+            for (x in xs.flatMap { it.toList() }) {
+                put(x, x.length)
+            }
+        }
+    }
+}