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

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

i18n/en.json

@@ -1150,6 +1150,7 @@
   "locked_folder": "Locked Folder",
   "log_out": "Log out",
   "log_out_all_devices": "Log Out All Devices",
+  "logged_in_as": "Logged in as {user}",
   "logged_out_all_devices": "Logged out all devices",
   "logged_out_device": "Logged out device",
   "login": "Login",
@@ -1607,6 +1608,7 @@
   "select_album_cover": "Select album cover",
   "select_all": "Select all",
   "select_all_duplicates": "Select all duplicates",
+  "select_all_in": "Select all in {group}",
   "select_avatar_color": "Select avatar color",
   "select_face": "Select face",
   "select_featured_photo": "Select featured photo",
@@ -1871,6 +1873,7 @@
   "unsaved_change": "Unsaved change",
   "unselect_all": "Unselect all",
   "unselect_all_duplicates": "Unselect all duplicates",
+  "unselect_all_in": "Unselect all in {group}",
   "unstack": "Un-stack",
   "unstacked_assets_count": "Un-stacked {count, plural, one {# asset} other {# assets}}",
   "up_next": "Up next",