API routes referencing a specific issue should use the issue `iid`

What does this MR do?

• Use Issues and MR iids instead of id for API v4 routes of the form /projects/:project_id/issues/:issue_id

Are there points in the code the reviewer needs to double check?

• Make sure there aren't any endpoints that need to be migrated to IID that aren't covered by this MR.
• Make sure v3 compatibility is maintained.

Why was this MR needed?

• This change makes the API more closely resemble the routes of the web interface.
• Since this is a breaking change, this should go into API v4.

Tasks

• Implementation
  • Modify routes in lib/api/issues
  • Modify routes in lib/api/merge_requests
  • Any other instances of :merge_request_id
    • Merge request diffs
    • Award emoji
    • Todos API
    • TimeTrackingEndpoints
  • Any other instances of :issue_id
    • Award emoji
    • Todos API
    • TimeTrackingEndpoints
• Tests
  • Added
  • Passing
• Meta
  • CHANGELOG entry created
  • Branch has no merge conflicts with master
  • Squashed related commits together
  • Added screenshots
  • Check for clean merge with EE
  • Documentation added/updated
    • Merge requests API
    • Issues API
    • Award emoji API
    • Todos API
    • Time tracking endpoints
    • Update v3-to-v4 document
• Follow-up
  • Sanity check from command line
  • Verify that V3 API is unaffected
    • Backport "time tracking endpoints" to v3
    • Any other V3 backports to be made?
  • Verify that award emoji conflict was resolved correctly
  • Verify that conflicts on EE branch were resolved correctly
• Review
  • Reviewer
  • Maintainer
• Wait for merge

---

• Closes #28251 (closed)
• Related EE MR: gitlab-org/gitlab-ee!1325

marked the task Investigation as completed

marked the task Find out which endpoints need to be modified as completed

added 2 commits

• 56b99e92 - API routes referencing a specific merge request should use the MR iid
• 700cf7b5 - Migrate the MergeRequestDiffs API to use merge_request_iid

Compare with previous version

added 2 commits

• 89577caf - Migrate the MergeRequestDiffs API to use merge_request_iid
• bf0762f2 - Migrate the AwardEmoji API to use merge_request_iid and issue_iid

Compare with previous version

added 110 commits

• bf0762f2...7733f285 - 105 commits from branch master
• 0c15fb68 - API routes referencing a specific issue should use the issue iid
• d503fae2 - API routes referencing a specific merge request should use the MR iid
• 23c2bb82 - Migrate the MergeRequestDiffs API to use merge_request_iid
• a3f187ea - Migrate the AwardEmoji API to use merge_request_iid and issue_iid
• 2c7e2b19 - Migrate the Todos API to use issuable_iid

Compare with previous version

added 1 commit

• 9e59ac03 - Fix time tracking endpoints for API v4

Compare with previous version

marked the task Implementation as completed

marked the task Any other instances of :merge_request_id as completed

marked the task TimeTrackingEndpoints as completed

marked the task Any other instances of :issue_id as completed

marked the task TimeTrackingEndpoints as completed

marked the task Tests as completed

marked the task Added as completed

marked the task Passing as completed

added 1 commit

• 54f22691 - Fix time tracking endpoints for API v4

Compare with previous version

added 27 commits

• 54f22691...58758bd5 - 21 commits from branch master
• 4fee990c - API routes referencing a specific issue should use the issue iid
• 57579eb6 - API routes referencing a specific merge request should use the MR iid
• 7071d714 - Migrate the MergeRequestDiffs API to use merge_request_iid
• b614eebf - Migrate the AwardEmoji API to use merge_request_iid and issue_iid
• f9afd07f - Migrate the Todos API to use issuable_iid
• b4a6fb55 - Fix time tracking endpoints for API v4

Compare with previous version

marked the task CHANGELOG entry created as completed

marked the task Branch has no merge conflicts with master as completed

marked the task Squashed related commits together as completed