Open entry editor by default on start-up

Fixes JabRef#5460

Select the first entry in the main table, and open entry editor
for the same. This action is performed on the application thread.

src/main/java/org/jabref/gui/BasePanel.java

@@ -178,6 +178,8 @@ public BasePanel(JabRefFrame frame, BasePanelPreferences preferences, BibDatabas
         this.getDatabase().registerListener(new UpdateTimestampListener(Globals.prefs));
 
         this.entryEditor = new EntryEditor(this, externalFileTypes);
+        // Open entry editor for first entry on start up.
+        Platform.runLater(() -> clearAndSelectFirst());
     }
 
     @Subscribe
@@ -867,6 +869,14 @@ public void clearAndSelect(final BibEntry bibEntry) {
         mainTable.clearAndSelect(bibEntry);
     }
 
+    /**
+     * Select and open entry editor for first entry in main table.
+     */
+    private void clearAndSelectFirst() {
+        mainTable.clearAndSelectFirst();
+        showAndEdit();
+    }
+
     public void selectPreviousEntry() {
         mainTable.getSelectionModel().clearAndSelect(mainTable.getSelectionModel().getSelectedIndex() - 1);
     }

src/main/java/org/jabref/gui/maintable/MainTable.java

@@ -206,7 +206,7 @@ private void setupKeyBindings(KeyBindingRepository keyBindings) {
         });
     }
 
-    private void clearAndSelectFirst() {
+    public void clearAndSelectFirst() {
         getSelectionModel().clearSelection();
         getSelectionModel().selectFirst();
         scrollTo(0);