[LL FIR] implement toString for LLFirKotlinSymbolProvider and LLFirSession

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/providers/LLFirKotlinSymbolProvider.kt

@@ -63,4 +63,8 @@ internal abstract class LLFirKotlinSymbolProvider(session: FirSession) : FirSymb
         callableId: CallableId,
         properties: Collection<KtProperty>,
     )
+
+    override fun toString(): String {
+        return "${this::class.simpleName} for $session"
+    }
 }

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/sessions/LLFirSession.kt

@@ -60,6 +60,10 @@ abstract class LLFirSession(
             return count.incrementAndGet()
         }
     }
+
+    override fun toString(): String {
+        return "${this::class.simpleName} for ${ktModule.moduleDescription}"
+    }
 }
 
 abstract class LLFirModuleSession(