KTIJ-33154 [kotlin] Consistently use cancelling processor in getAllElements

In cases when `SubKey` is a very small percentage of all possible results
collected by `processAllElements`, simply returning `true` from processing without
any cancellation checks can be problematic.

This change makes sure that `processor` with cancellation checks
is consistently used for every processed result.

The downside is that now we have to use unchecked cast
of a collection.

GitOrigin-RevId: d475d20b0d4df33f8aff7cf65eb7b79659b40cf9

plugins/kotlin/base/indices/src/org/jetbrains/kotlin/idea/stubindex/KotlinStringStubIndexHelper.kt

@@ -78,15 +78,14 @@ abstract class KotlinStringStubIndexHelper<Key : NavigatablePsiElement>(private
         noinline keyFilter: (String) -> Boolean = { true },
         noinline valueFilter: (SubKey) -> Boolean = { true },
     ): Sequence<SubKey> {
-        val results = mutableListOf<SubKey>()
-        val processor = cancelableCollectFilterProcessor(results, filter = valueFilter)
-        processAllElements(project, scope, keyFilter) { key ->
-            if (key is SubKey)
-                processor.process(key)
-            else
-                true
-        }
-        return results.asSequence() // todo move valueFilter out
+        val results = mutableListOf<Any>()
+        val processor = cancelableCollectFilterProcessor(results) { key -> key is SubKey && valueFilter(key) }
+
+        processAllElements(project, scope, keyFilter, processor)
+
+        @Suppress("UNCHECKED_CAST")
+        val castedResults = results as List<SubKey>
+        return castedResults.asSequence() // todo move valueFilter out
     }
 
     fun processAllElements(