some changes introduced by 4daa6da5407d235cbe4f7a787eaa29304446a870, 26b6e299e1c97b956306572c5c9f6c02f428bfd7, 17898ce021fc365c620d4600df68c3e7d2151619 were regressed during today's merge conflict resolution of !11573.

This commit serves to reapply those changes.

/cc: @rspeicher @stanhu @mikegreiling

Include new URL helpers retroactively into includers of Gitlab::Routing

Closes #34821

See merge request !12716

Don't mark empty MRs as merged on push to the target branch

Closes #32800

See merge request !12711

When we push to an MR's target branch, we check if the MR's HEAD commit is
contained in the push. This lets us mark MRs as merged if they were merged
manually.

However, we also added a feature where you can create an empty MR from an
issue. If that MR is created around the time of a merge to the default branch,
we would process the push after creating the MR, and consider it to be a manual
merge.

To fix that, we exclude empty MRs from this process. If they are empty, they
were empty before the push we're processing, so we shouldn't touch them!

This makes the `Boards::CreateService` more reusable for EE

See merge request !12704