Merge branch 'explain-code-highlight-lines' into 'master'

Code explanation: Highlight selected code lines

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/121830



Merged-by: Jacques Erasmus <jerasmus@gitlab.com>
Approved-by: Annabel Dunstone Gray <annabel.dunstone@gmail.com>
Approved-by: Jacques Erasmus <jerasmus@gitlab.com>
Reviewed-by: Jacques Erasmus <jerasmus@gitlab.com>
Reviewed-by: Nataliia Radina <nradina@gitlab.com>
Co-authored-by: Nataliia Radina <nradina@gitlab.com>
Co-authored-by: Sascha Eggenberger <seggenberger@gitlab.com>