FIR IDE: make smartcast API return unstable smartcasts

analysis/analysis-api/testData/components/smartCastInfo/multiSmartcastAsReceiver_stable.kt

@@ -0,0 +1,10 @@
+interface A
+interface B
+
+fun <T> T.foo() where T: A, T: B {}
+
+fun test(a: Any) {
+    if (a is A && a is B) {
+        <expr>a</expr>.foo()
+    }
+}