Prepare code for jQuery 3.x

[kouralex]

This PR mitigates warnings related to jQuery 3.x upgrade that were encountered whilst testing the product with jQuery 3.6.0 and jQuery Migrate 3.3.2 plugin. Additionally, fixes some validator.w3.org warnings.

Next step: replace/upgrade libraries that depend on jQuery 2.x or cause hassle, list includes (but is not necessarily limited to):

• malihu/malihu-custom-scrollbar-plugin (visible difference between jQuery 2.x and 3.x)
• grimmlink/qtip2 (jQuery migration plugin warnings)
• twitter/typeahead.js (jQuery migration plugin warnings)
• twitter/bootstrap (jQuery migration plugin warnings)
• etdsolutions/waypoints (jQuery migration plugin warnings)
• vakata/jstree (jQuery migration plugin warnings)

Some of these "only" use deprecated features that are not per se dangerous and jQuery Migrate plugin (which restores old API) can be used in production for a while. See https://github.com/jquery/jquery-migrate/blob/main/warnings.md for more information.

Additional info: https://jquery.com/upgrade-guide/3.0/ and https://jquery.com/upgrade-guide/3.5/

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Merging #1144 (1c02a27) into master (d904172) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1144   +/-   ##
=========================================
  Coverage     67.96%   67.96%           
  Complexity     1584     1584           
=========================================
  Files            32       32           
  Lines          3889     3889           
=========================================
  Hits           2643     2643           
  Misses         1246     1246           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d904172...1c02a27. Read the comment docs.

[kinow]

So many tags without closing 😄 . Looks good to me!

Tested with Docker, loaded the two vocabularies for the test, successfully navigated the UI, used the search dropdown, changed language. No issues found.

[osma]

Looks good to me too!

[kouralex]

Thank you for reviewing! :)