* Added new serializers for Issue and MergeRequest.

Also added new attributes related to time tracking to the JSON payload.

This flag will be used to properly update the sidebar after the slash
commands have been processed.

I've also applied other minor refactorings and fixed a broken spec.

This is to have consistency with the #time_spent method on Issuables
that returns 0 when the user has not entered any info about it.

This method returns the total spent time that the user has declared
through the `/spend` slash command.

[ci skip]

[ci skip]

[ci skip]

[ci skip]

Remove order-dependent expectation

Fixes #24341, hopefully

See merge request !7385

CE Upstream

See merge request !859