Edit Mode: respect modifier keys in hotkeys, add message duration, and helper refactors

Problem/Motivation

Several small, independent Edit Mode issues had accumulated:

• Tool hotkeys swallow browser/OS shortcuts. The keydown
  handler matched a single character against the tool hotkey map without
  checking modifier keys, so combinations such as Ctrl/Cmd+R could
  activate a tool instead of performing the browser action.
• Edit Mode messages have no configurable lifetime.
  EditModeMessageCommand always used the client's per-type default
  duration, with no way for the server to request a shorter or permanent
  message.
• The entity wrapper id format was duplicated. The
  entity_type::identifier::bundle string used to target an entity's
  editable wrapper in AJAX refreshes was built inline in more than one place, so
  producers and consumers could drift.
• _navigation_plus_get_entity_view_display() assumed a
  display always exists. Config entities have no view display, so the
  non-nullable return type was incorrect.

User interface changes

Browser and OS keyboard shortcuts are no longer intercepted by tool hotkeys
while Edit Mode is active. We will be switching out this hotkey functionality for something more robust pretty soon.

API changes

• EditModeMessageCommand::__construct() gains an optional
  ?int $duration = NULL parameter.
• New navigation_plus_entity_wrapper_id(EntityInterface $entity): string.
• _navigation_plus_get_entity_view_display() return type widened
  to ?EntityViewDisplayInterface.