[FIR] Don't constraints for return expressions of lambda if it has Unit return type

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/builderInferenceAndCoercionToUnit.kt

@@ -0,0 +1,9 @@
+class DropDownComponent<T : Any>(val initialValues: List<T>)
+
+fun test(strings: List<String>) {
+    val dropDown = DropDownComponent(
+        initialValues = buildList {
+            addAll(strings)
+        }
+    )
+}

compiler/fir/analysis-tests/testData/resolveWithStdlib/inference/builderInferenceAndCoercionToUnit.txt

@@ -0,0 +1,16 @@
+FILE: builderInferenceAndCoercionToUnit.kt
+    public final class DropDownComponent<T : R|kotlin/Any|> : R|kotlin/Any| {
+        public constructor<T : R|kotlin/Any|>(initialValues: R|kotlin/collections/List<T>|): R|DropDownComponent<T>| {
+            super<R|kotlin/Any|>()
+        }
+
+        public final val initialValues: R|kotlin/collections/List<T>| = R|<local>/initialValues|
+            public get(): R|kotlin/collections/List<T>|
+
+    }
+    public final fun test(strings: R|kotlin/collections/List<kotlin/String>|): R|kotlin/Unit| {
+        lval dropDown: R|DropDownComponent<kotlin/String>| = R|/DropDownComponent.DropDownComponent|<R|kotlin/String|>(initialValues = R|kotlin/collections/buildList|<R|kotlin/String|>(<L> = buildList@fun R|kotlin/collections/MutableList<kotlin/String>|.<anonymous>(): R|kotlin/Unit| <kind=EXACTLY_ONCE>  {
+            this@R|special/anonymous|.R|FakeOverride<kotlin/collections/MutableList.addAll: R|kotlin/Boolean|>|(R|<local>/strings|)
+        }
+        ))
+    }