Expose `lines_added` and `lines_removed` in Merge Requests API
> Note: Issues applies to MR API in both CE and EE. Issue created in EE in anticipation of merging of project issue trackers ### Problem to solve Determine the size of a Merge Request via the API ### Proposal Add `lines_added` and `lines_removed` to the MR API entity. ### Permissions and Security Existing MR authorization checks will cover this ### Documentation API documentation updates required ### What is the type of buyer? Core ### Links / references
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