Feature/4717 accessibility improvements aria tags

[robinmolen]

Closes open-formulieren/open-forms#4717

Some accessibility improvements involving aria tags, role's and textual alternatives:

• The Loader element now has a textual alternative, which will be translated.
• The modals now use html buttons as buttons (instead of icons with a button role).
• The delete button/link for an file now specifies which file will be removed.
• And finally alerts now have role="alert".

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.42%. Comparing base (ee809c9) to head (8db4908).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #719      +/-   ##
==========================================
- Coverage   77.56%   77.42%   -0.15%     
==========================================
  Files         233      233              
  Lines        4752     4775      +23     
  Branches     1283     1302      +19     
==========================================
+ Hits         3686     3697      +11     
- Misses       1033     1045      +12     
  Partials       33       33              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.