[FIR] Render dot-separated FQNs instead of slash-separated ones in diagnostics

^KT-62030 fixed

compiler/testData/diagnostics/tests/resolve/specialConstructions/elvisAsCall.fir.kt

@@ -13,7 +13,7 @@ fun testElvis(a: Int?, b: Int?) {
     if (a != null) {
         doInt(b ?: a)
     }
-    <!INFERRED_TYPE_VARIABLE_INTO_POSSIBLE_EMPTY_INTERSECTION("T; a/A, kotlin/Int; final class and interface")!>doList<!>(getList() ?: emptyListOfA()) //should be an error
+    <!INFERRED_TYPE_VARIABLE_INTO_POSSIBLE_EMPTY_INTERSECTION("T; a.A, kotlin.Int; final class and interface")!>doList<!>(getList() ?: emptyListOfA()) //should be an error
     doList(getList() ?: strangeList { doInt(it) }) //lambda was not analyzed
 }