feat: show error notifications from extensions

fix #268

Author: sqs

src/libs/code_intelligence/extensions.tsx

@@ -1,4 +1,5 @@
 import { CommandListPopoverButton } from '@sourcegraph/extensions-client-common/lib/app/CommandList'
+import { Notifications } from '@sourcegraph/extensions-client-common/lib/app/notifications/Notifications'
 import {
     Controller as ClientController,
     createController,
@@ -118,6 +119,7 @@ export function initializeExtensions(
                 menu={ContributableMenu.CommandPalette}
                 extensions={extensionsContextController}
             />
+            <Notifications extensionsController={extensionsController} />
         </ShortcutProvider>,
         getCommandPaletteMount()
     )

src/shared/extensions-client-common.scss

@@ -2,6 +2,8 @@
 @import '@sourcegraph/extensions-client-common/lib/ui/generic/Toggle.css';
 @import '@sourcegraph/extensions-client-common/lib/app/CommandList';
 @import '@sourcegraph/extensions-client-common/lib/app/ExtensionStatus';
+@import '@sourcegraph/extensions-client-common/lib/app/notifications/Notifications';
+@import '@sourcegraph/extensions-client-common/lib/app/notifications/NotificationItem';
 @import '@sourcegraph/extensions-client-common/lib/extensions/manager/ExtensionCard.css';
 
 $body-color-light: #2b3750;