Devirtualization fails to eliminate boxing in function reference context

^KT-49847 Fixed

Merge-request: KT-MR-6460
Merged-by: Vladimir Sukharev <Vladimir.Sukharev@jetbrains.com>

compiler/testData/codegen/box/reflection/genericSignature/genericFunctionReferenceSignature.kt

@@ -0,0 +1,12 @@
+// WITH_REFLECT
+
+package test
+
+fun <T> foo(x: T) = x
+
+fun box(): String {
+    val bar: kotlin.reflect.KFunction1<Int, Int> = ::foo
+    val returnType = bar.returnType
+    if (returnType.toString() != "T") return returnType.toString()
+    return "OK"
+}