FIR: add test fixing builder inference case

compiler/fir/analysis-tests/testData/resolveWithStdlib/problems/KtFirCompositeScope.kt

@@ -0,0 +1,19 @@
+interface KtScope {
+    fun getAllNames(): Set<String>
+}
+
+inline fun <E> buildSet(@BuilderInference builderAction: MutableSet<E>.() -> Unit): Set<E> {
+    return null!!
+}
+
+inline fun <R> withValidityAssertion(action: () -> R): R {
+    return action()
+}
+
+class KtFirCompositeScope(val subScopes: List<KtScope>) {
+    fun getAllNames(): Set<String> = withValidityAssertion {
+        buildSet {
+            subScopes.flatMapTo(this) { it.getAllNames() }
+        }
+    }
+}