FIR: use expected type for lambda return statements if possible

compiler/testData/diagnostics/tests/inference/coercionToUnit/nestedLambda.kt

@@ -0,0 +1,20 @@
+// FIR_IDENTICAL
+// !SKIP_TXT
+interface Context<T> {
+    fun proceed(): T
+}
+
+interface A<T : Any, K : Any> {
+    fun process(block: Context<T>.(T) -> Unit)
+}
+
+fun <T> processNested(body: () -> T): T {
+    return body()
+}
+
+fun test(pipeline: A<Any, String>) {
+    pipeline.process {
+        // OK: processNested<Unit> { /* no return */ proceed() /*: Any */ /* implicit coercion to Unit */ }
+        return@process processNested { proceed() }
+    }
+}