suggest after import prefix in part files - fixes #25023

pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart

Index: pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
diff --git a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
index cf3b798edfe1619a10e80e924e7795e39a8bd4c5..03464dcbbac93b3d916b46b66522db751f4a9190 100644
--- a/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
+++ b/pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart
@@ -92,6 +92,16 @@ abstract class DartCompletionRequest extends CompletionRequest {
   Future<CompilationUnit> resolveDeclarationsInScope();
 
   /**
+   * Return a [Future] that completes with a list of directives for the library
+   * in which in which the completion is occurring.
+   * The [Future] may return `null` if the library unit cannot be determined
+   * (e.g. unlinked part file).
+   * Any information obtained from [target] prior to calling this method
+   * should be discarded as it may have changed.
+   */
+  Future<List<Directive>> resolveDirectives();
+
+  /**
    * Return a [Future] that completes when the element associated with
    * the given [expression] in the target compilation unit is available.
    * It may also complete if the expression cannot be resolved