Viewer: Add a keyboard shortcut (Ctrl+w) to toggle the scrollbar. Fixes #1864356 [[Enhancement] Hide scrollbar by right clicking on it](https://bugs.launchpad.net/calibre/+bug/1864356)

src/calibre/gui2/viewer/ui.py

@@ -210,6 +210,8 @@ class EbookViewer(MainWindow):
         m.addSeparator()
         a(_('Start of current file'), 'start_of_file')
         a(_('End of current file'), 'end_of_file')
+        m.addSeparator()
+        a(_('Hide this scrollbar'), 'toggle_scrollbar')
 
         q = m.exec_(QCursor.pos())
         if not q:

src/pyj/read_book/shortcuts.pyj

@@ -228,6 +228,12 @@ def shortcuts_definition():
         _('Toggle between Paged mode and Flow mode for text layout')
     ),
 
+    'toggle_scrollbar': desc(
+        'Ctrl+w',
+        'ui',
+        _('Toggle the scrollbar')
+    ),
+
     'toggle_reference_mode': desc(
         'Ctrl+x',
         'ui',

src/pyj/read_book/view.pyj

@@ -269,6 +269,15 @@ class View:
     def reference_mode_overlay(self):
         return document.getElementById('reference-mode-overlay')
 
+    def set_scrollbar_visibility(self, visible):
+        sd = get_session_data()
+        sd.set('book_scrollbar', bool(visible))
+        self.book_scrollbar.apply_visibility()
+
+    def toggle_scrollbar(self):
+        sd = get_session_data()
+        self.set_scrollbar_visibility(not sd.get('book_scrollbar'))
+
     def on_lookup_word(self, data):
         if runtime.is_standalone_viewer:
             ui_operations.selection_changed(data.word)
@@ -388,6 +397,8 @@ class View:
             self.toggle_paged_mode()
         elif data.name is 'toggle_toolbar':
             self.toggle_toolbar()
+        elif data.name is 'toggle_scrollbar':
+            self.toggle_scrollbar()
         elif data.name is 'quit':
             ui_operations.quit()
         elif data.name is 'start_search':