[FIR] Type "top-level classifier names in package" as Name

- This is more consistent with "top-level callable names in package" and
  simplifies the set construction quite a bit, as we can avoid a lot of
  `asString` conversions.

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/providers/impl/FirCloneableSymbolProvider.kt

@@ -79,9 +79,9 @@ class FirCloneableSymbolProvider(
     }
 
     override val symbolNamesProvider: FirSymbolNamesProvider = object : FirSymbolNamesProviderWithoutCallables() {
-        override fun getTopLevelClassifierNamesInPackage(packageFqName: FqName): Set<String> =
+        override fun getTopLevelClassifierNamesInPackage(packageFqName: FqName): Set<Name> =
             if (packageFqName == StandardClassIds.Cloneable.packageFqName) {
-                setOf(StandardClassIds.Cloneable.shortClassName.asString())
+                setOf(StandardClassIds.Cloneable.shortClassName)
             } else emptySet()
     }
 

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/providers/impl/FirProviderImpl.kt

@@ -85,8 +85,8 @@ class FirProviderImpl(val session: FirSession, val kotlinScopeProvider: FirKotli
             override fun getPackageNamesWithTopLevelCallables(): Set<String> =
                 state.allSubPackages.mapTo(mutableSetOf()) { it.asString() }
 
-            override fun getTopLevelClassifierNamesInPackage(packageFqName: FqName): Set<String> =
-                state.classifierInPackage[packageFqName].orEmpty().mapTo(mutableSetOf()) { it.asString() }
+            override fun getTopLevelClassifierNamesInPackage(packageFqName: FqName): Set<Name> =
+                state.classifierInPackage[packageFqName].orEmpty()
 
             override fun getTopLevelCallableNamesInPackage(packageFqName: FqName): Set<Name> = buildSet {
                 for (key in state.functionMap.keys) {