Migrate icons to use new work items naming

Summary

In gitlab-svgs!1160 (merged) we added new icons to replace the existing issue-type icons as we introduce the work items concept (see gitlab-svgs#438 (moved)). This issue is to update the references in the product which use the previous issue-type icons to the new work-item svgs. After we have updated these in the product and confirm everything is good—we can move forward with deprecating / removing the legacy icons.

Important

This work is blocked by #526952 (closed), which should occur first. That will ensure all instances of the issues (or issue-type-issue) icon are updated at the same time in the product to the new version of the icon (which is a different design).

Implementation

Update the following icon references in the product:

legacy replacement
issue-type-enhancement work-item-enhancement
issue-type-feature-flag work-item-feature-flag
issue-type-feature work-item-feature
issue-type-incident work-item-incident
issue-type-issue work-item-issue
issue-type-keyresult work-item-keyresult
issue-type-maintenance work-item-maintenance
issue-type-objective work-item-objective
issue-type-requirements work-item-requirement
issue-type-task work-item-task
issue-type-test-case work-item-test-case
issue-type-ticket work-item-ticket

Additional icons to be updated

The following icons were not using issue-type icons previously, but should be updated with this work as we introduced new icons to cover them with the updated terminology and reorganization.

legacy replacement
issue-new work-item-new
epic work-item-epic
Edited by 🤖 GitLab Bot 🤖