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

^KT-62030 fixed

analysis/low-level-api-fir/testData/contextCollector/localClass.txt

@@ -22,7 +22,7 @@ Tower Data Context:
     Element 9
         Implicit receiver:
             FirRegularClassSymbol local final class Local : R|kotlin/Any|
-                Type: <local>/Local
+                Type: <local>.Local
     Element 10
         Scope: FirLocalScope
     Element 11
@@ -42,4 +42,4 @@ FILE: [ResolvedTo(IMPORTS)] localClass.kt
         }
 
         R|<local>/Local.Local|().R|<local>/foo|()
-    }
+    }