fix: EditorContextMenuPlugin with slot CONTEXT_SLOT_FILESYSTEM_CREATE does not add popup item to all menu

As there are multiple menu containing creating new files, this commit add the popup menu item from the plugin to all those menu to keep consistency.
The fixing uses empty array to indicate different types of context menu.

Added to these menu:
* Right-click on empty space on the tree (`_tree_empty_click`).
* Right-click on empty space on the file panel (`_file_list_empty_clicked`)

Also add explanation in `EditorContextMenuPlugin::CONTEXT_SLOT_FILESYSTEM_CREATE`'s doc for previous fixing

(Accept PR #106811 code suggestion by: Tomasz Chabora <[email protected]>)

doc/classes/EditorContextMenuPlugin.xml

@@ -89,7 +89,7 @@
 			Context menu of Script editor's script tabs. [method _popup_menu] will be called with the path to the currently edited script, while option callback will receive reference to that script.
 		</constant>
 		<constant name="CONTEXT_SLOT_FILESYSTEM_CREATE" value="3" enum="ContextMenuSlot">
-			The "Create..." submenu of FileSystem dock's context menu. [method _popup_menu] and option callback will be called with list of paths of the currently selected files.
+			The "Create..." submenu of FileSystem dock's context menu, or the "New" section of the main context menu when empty space is clicked. [method _popup_menu] and option callback will be called with list of paths of the currently selected files. When clicking the empty space, the list of paths for popup method will be empty.
 		</constant>
 		<constant name="CONTEXT_SLOT_SCRIPT_EDITOR_CODE" value="4" enum="ContextMenuSlot">
 			Context menu of Script editor's code editor. [method _popup_menu] will be called with the path to the [CodeEdit] node. You can fetch it using this code:

editor/filesystem_dock.cpp

@@ -3524,6 +3524,8 @@ void FileSystemDock::_tree_empty_click(const Vector2 &p_pos, MouseButton p_butto
 	tree_popup->add_icon_item(get_editor_theme_icon(SNAME("Script")), TTRC("New Script..."), FILE_MENU_NEW_SCRIPT);
 	tree_popup->add_icon_item(get_editor_theme_icon(SNAME("Object")), TTRC("New Resource..."), FILE_MENU_NEW_RESOURCE);
 	tree_popup->add_icon_item(get_editor_theme_icon(SNAME("TextFile")), TTRC("New TextFile..."), FILE_MENU_NEW_TEXTFILE);
+	// To keep consistency with options added to "Create New..." menu (for plugin which has slot as CONTEXT_SLOT_FILESYSTEM_CREATE).
+	EditorContextMenuPluginManager::get_singleton()->add_options_from_plugins(tree_popup, EditorContextMenuPlugin::CONTEXT_SLOT_FILESYSTEM_CREATE, Vector<String>());
 #if !defined(ANDROID_ENABLED) && !defined(WEB_ENABLED)
 	// Opening the system file manager is not supported on the Android and web editors.
 	tree_popup->add_separator();
@@ -3594,6 +3596,8 @@ void FileSystemDock::_file_list_empty_clicked(const Vector2 &p_pos, MouseButton
 	file_list_popup->add_icon_item(get_editor_theme_icon(SNAME("Script")), TTRC("New Script..."), FILE_MENU_NEW_SCRIPT);
 	file_list_popup->add_icon_item(get_editor_theme_icon(SNAME("Object")), TTRC("New Resource..."), FILE_MENU_NEW_RESOURCE);
 	file_list_popup->add_icon_item(get_editor_theme_icon(SNAME("TextFile")), TTRC("New TextFile..."), FILE_MENU_NEW_TEXTFILE);
+	// To keep consistency with options added to "Create New..." menu (for plugin which has slot as CONTEXT_SLOT_FILESYSTEM_CREATE).
+	EditorContextMenuPluginManager::get_singleton()->add_options_from_plugins(file_list_popup, EditorContextMenuPlugin::CONTEXT_SLOT_FILESYSTEM_CREATE, Vector<String>());
 	file_list_popup->add_separator();
 	file_list_popup->add_icon_shortcut(get_editor_theme_icon(SNAME("Terminal")), ED_GET_SHORTCUT("filesystem_dock/open_in_terminal"), FILE_MENU_OPEN_IN_TERMINAL);
 	file_list_popup->add_icon_shortcut(get_editor_theme_icon(SNAME("Filesystem")), ED_GET_SHORTCUT("filesystem_dock/show_in_explorer"), FILE_MENU_SHOW_IN_EXPLORER);