feat: improve mobile screen reader accessibility (#17876)

* WIP: adding screen reader support to mobile

* implemented getAltText

* implemented alt text solution that stores the alt text in the DB, which isn't really great

* moved alt text computation to immich_thumbnail.dart

* added unit tests

* revert unintended changes

* Added text to remaining buttons in Photo page

* fixed import

* Fixed issue of easy_localization not parsing select blocks

* Transferred the new screen reader help to web frontend

* remove unused property

* npm run format:fix

* code review

* revert unwanted change

* dart fmt

* revert web changes

---------

Co-authored-by: shenlong-tanwen <139912620+shalong-tanwen@users.noreply.github.com>

mobile/lib/widgets/common/immich_app_bar.dart

@@ -66,10 +66,13 @@ class ImmichAppBar extends ConsumerWidget implements PreferredSizeWidget {
                   Icons.face_outlined,
                   size: widgetSize,
                 )
-              : UserCircleAvatar(
-                  radius: 17,
-                  size: 31,
-                  user: user,
+              : Semantics(
+                  label: "logged_in_as".tr(namedArgs: {"user": user.name}),
+                  child: UserCircleAvatar(
+                    radius: 17,
+                    size: 31,
+                    user: user,
+                  ),
                 ),
         ),
       );