K2: Optimize AbstractFirDeserializedSymbolProvider

Avoid filling caches with keys that are definitely empty
(if it's cheap to compute that), to decrease the size of backing maps.

The strategy is pre-computing the sets of names that might be met.
NB: the size of the sets is way fewer than a size of all queried names.

core/descriptors.jvm/src/org/jetbrains/kotlin/load/kotlin/JvmPackagePartProviderBase.kt

@@ -39,6 +39,11 @@ abstract class JvmPackagePartProviderBase<MappingsKey> : PackagePartProvider, Me
         return result.toList()
     }
 
+    private val allPackageNames: Set<String> by lazy {
+        loadedModules.flatMapTo(mutableSetOf()) { it.mapping.packageFqName2Parts.keys }
+    }
+
+    override fun computePackageSetWithNonClassDeclarations(): Set<String> = allPackageNames
     override fun findMetadataPackageParts(packageFqName: String): List<String> =
         getPackageParts(packageFqName).flatMap(PackageParts::metadataParts).distinct()