Added <any file type> to the Import File Filter Dialog.

CHANGELOG.md

@@ -12,6 +12,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 ## [Unreleased]
 
 ### Changed
+- Added "*.*" (any file type) to the Import File Filter Dialog. [#3757] (https://github.com/JabRef/jabref/issues/3757)
 - Abbreviate journal names functionality is now running parallel, increasing performance significantly. [#2831] (https://github.com/JabRef/jabref/issues/2831)
 - Changed order of items in context menu [#298] (https://github.com/koppor/jabref/issues/298)
 - Changed ID-based entry generator to store the last used fetcher. [#2796] (https://github.com/JabRef/jabref/issues/2796)

src/main/java/org/jabref/gui/importer/ImportFormats.java

@@ -67,12 +67,12 @@ public void actionPerformed(ActionEvent e) {
                 List<FileType> extensions = importers.stream().map(Importer::getFileType)
                         .collect(Collectors.toList());
                 FileChooser.ExtensionFilter allImports = FileFilterConverter.forAllImporters(importers);
-
                 FileDialogConfiguration fileDialogConfiguration = new FileDialogConfiguration.Builder()
                         .addExtensionFilter(allImports)
                         .addExtensionFilters(extensions)
                         .withInitialDirectory(Globals.prefs.get(JabRefPreferences.IMPORT_WORKING_DIRECTORY))
                         .build();
+                fileDialogConfiguration.getExtensionFilters().add(new FileChooser.ExtensionFilter("Any file", "*.*"));
                 DialogService dialogService = new FXDialogService();
                 DefaultTaskExecutor.runInJavaFXThread(() -> {
                     dialogService.showFileOpenDialog(fileDialogConfiguration)