[FIR] Force calculation of return type of fake overrides in return type calculator

compiler/fir/analysis-tests/testData/resolve/implicitTypeInFakeOverride.kt

@@ -3,3 +3,7 @@ fun <K> extract(x: Out<K>) = x.get()
 class Out<out T>(val x: T) {
     fun get() = x
 }
+
+fun test(out: Out<String>) {
+    <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.String")!>extract(out)<!>
+}

compiler/fir/analysis-tests/testData/resolve/implicitTypeInFakeOverride.txt

@@ -1,6 +1,6 @@
 FILE: implicitTypeInFakeOverride.kt
-    public final fun <K> extract(x: R|Out<K>|): R|T| {
-        ^extract R|<local>/x|.R|/Out.get|()
+    public final fun <K> extract(x: R|Out<K>|): R|K| {
+        ^extract R|<local>/x|.R|FakeOverride</Out.get: R|K|>|()
     }
     public final class Out<out T> : R|kotlin/Any| {
         public constructor<out T>(x: R|T|): R|Out<T>| {
@@ -15,3 +15,6 @@ FILE: implicitTypeInFakeOverride.kt
         }
 
     }
+    public final fun test(out: R|Out<kotlin/String>|): R|kotlin/Unit| {
+        R|/extract|<R|kotlin/String|>(R|<local>/out|)
+    }