try intersection of upper bounds as a suggestion

not each bound itself
while resolving constraint system

compiler/testData/diagnostics/tests/inference/upperBounds/nonNullUpperBound.kt

@@ -0,0 +1,13 @@
+fun <R : Any> unescape(value: Any): R? = throw Exception("$value")
+
+fun <T: Any> foo(v: Any): T? = unescape(v)
+
+//--------------
+
+trait A
+
+fun <R : A> unescapeA(value: Any): R? = throw Exception("$value")
+
+
+fun <T: A> fooA(v: Any): T? = unescapeA(v)
+