Clarify which project is deleted to avoid alarm

Some users were alarmed when navigating after deleting  a project. Add the project name to avoid cause for alarm.

Closes #13654 

See merge request !5574

Properly abort a merge when merge conflicts occur

If somehow a user attempted to accept a merge request that had conflicts (e.g. the "Accept Merge Request" button or the MR itself was not updated), `MergeService` did not properly detect that a conflict
occurred. It would assume that the MR went through without any issues and close the MR as though everything was fine. This could cause data loss if the source branch were removed.

Closes #20425

See merge request !5569

Improve diff performance by eliminating redundant checks for text blobs

See merge request !5575

On a merge request with over 1000 changed files, there were redundant
calls to blob_text_viewable?, which incurred about 7% of the time.

Improves #14775

Closes #13654

If somehow a user attempted to accept a merge request that had
conflicts (e.g. the "Accept Merge Request" button or the MR itself was
not updated), `MergeService` did not properly detect that a conflict
occurred. It would assume that the MR went through without any issues
and close the MR as though everything was fine. This could cause
data loss if the source branch were removed.

Closes #20425

fix repo hooks missing on import

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19556 

Repo hooks are missing from imported projects

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5549

Optimize checking if a user can read multiple issues

## What does this MR do?

This optimizes various parts of the code so it can more efficiently check if a user can read a list of issues.

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

Yes, in particular `Ability.issues_readable_by_user` should be checked to make sure it correctly allows/restricts access to issues.

## Why was this MR needed?

Currently the general approach to checking if one can read an issue is to iterate over the issues to check and call `can?(user, :read_issue, issue)` for every issue. This is not efficient as the same work has to be done for every issue.

## What are the relevant issue numbers?

* #15607 
* #17463

See merge request !5370

Enable Rubocop cops that check access modifiers

## What does this MR do?

This MR enables Rubocop cops that detect methods that should be restricted but are the part of public API because of access modifiers used improperly.

This also fixes existing offenses.

## Why was this MR needed?

Some method in our codebase are public instead of being private because it is sometimes difficult to get it right without static analysis.

## What are the relevant issue numbers?

See #17478  
Closes #17372 

See merge request !5014

Move CI job config entries from legacy to new config

## What does this MR do?

This MR extracts jobs configuration logic from legacy CI config processor to the new code.

## What are the relevant issue numbers?

#15060

## Does this MR meet the acceptance criteria?

- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)

See merge request !5087

Check for Ci::Build artifacts at database level

## What does this MR do?

Check for the presence of artifacts not expired at database level

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

N/A

## Why was this MR needed?

To try to improve a little the performance of the pipelines page

## What are the relevant issue numbers?

Closes #20371

## Screenshots (if relevant)

N/A

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5543

Bump gitlab_git to speedup DiffCollection iterations

See merge request !5564

The method Ability.issues_readable_by_user takes a list of users and an
optional user and returns an Array of issues readable by said user. This
method in turn is used by
Banzai::ReferenceParser::IssueParser#nodes_visible_to_user so this
method no longer needs to get all the available abilities just to check
if a user has the "read_issue" ability.

To test this I benchmarked an issue with 222 comments on my development
environment. Using these changes the time spent in nodes_visible_to_user
was reduced from around 120 ms to around 40 ms.