Fix #1921572 [[Viewer] Ctrl+A doesn't work when some text is selected](https://bugs.launchpad.net/calibre/+bug/1921572)

src/pyj/read_book/iframe.pyj

@@ -185,6 +185,12 @@ class IframeBoss:
 
     def modify_selection(self, data):
         sel = window.getSelection()
+        if data.granularity is 'all':
+            r = document.createRange()
+            r.selectNode(document.body)
+            sel.removeAllRanges()
+            sel.addRange(r)
+        else:
             try:
                 sel.modify('extend', data.direction, data.granularity)
             except:

src/pyj/read_book/selection_bar.pyj

@@ -581,6 +581,7 @@ class SelectionBar:
         forwarded = {
             'toggle_highlights': True,
             'edit_book': True,
+            'select_all': True,
         }
         if sc_name is 'show_chrome':
             self.clear_selection()

src/pyj/read_book/shortcuts.pyj

@@ -344,6 +344,12 @@ def common_shortcuts():  # {{{
         _('Alter the current selection forward by a line'),
     ),
 
+    'select_all': desc(
+        v'["Ctrl+a"]',
+        'ui',
+        _('Select all')
+    ),
+
     'shrink_selection_by_line': desc(
         v"['Shift+ArrowUp']",
         'ui',

src/pyj/read_book/view.pyj

@@ -559,6 +559,8 @@ class View:
             ui_operations.edit_book(current_spine_item(), self.current_file_progress_frac, self.currently_showing?.selection?.text)
         elif data.name is 'goto_location':
             self.overlay.show_ask_for_location()
+        elif data.name is 'select_all':
+            self.iframe_wrapper.send_message('modify_selection', granularity='all')
         elif data.name.startsWith('shrink_selection_by_'):
             self.iframe_wrapper.send_message('modify_selection', direction='backward', granularity=data.name.rpartition('_')[-1])
         elif data.name.startsWith('extend_selection_by_'):