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.

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/incremental/IncrementalPackagePartProvider.kt

@@ -52,6 +52,15 @@ class IncrementalPackagePartProvider(
                 parent.findPackageParts(packageFqName)).distinct()
     }
 
+    private val allPackageNames: Set<String> by lazy {
+        buildSet {
+            moduleMappings.flatMapTo(this@buildSet) { it.packageFqName2Parts.keys }
+            addAll(parent.computePackageSetWithNonClassDeclarations())
+        }
+    }
+
+    override fun computePackageSetWithNonClassDeclarations(): Set<String> = allPackageNames
+
     override fun getAnnotationsOnBinaryModule(moduleName: String): List<ClassId> {
         return parent.getAnnotationsOnBinaryModule(moduleName)
     }