Resolve "Destroying a project causes post_decline_request to be executed"

## What does this MR do?

Ensure we don't send "access request declined" to access requesters when a project is deleted.

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

I've created a service to decouple the notification sending from the AR model.

## Why was this MR needed?

Because there was an issue.

## What are the relevant issue numbers?

Fixes #18755, #18750.

## Does this MR meet the acceptance criteria?

- [x] No CHANGELOG needed.
- [x] 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 !4744

Optimize Banzai::Filter::RelativeLinkFilter

See merge request !4813

    A lot of git operations were being repeated, for example, to build a url
    you would ask if the path was a Tree, which would call a recursive routine
    in Gitlab::Git::Tree#where, then ask if the path was a Blob, which would
    call a recursive routine at Gitlab::Git::Blob#find, making reference to
    the same git objects several times. Now we call Rugged::Tree#path, which
    allows us to determine the type of the path in one pass.

    Some other minor improvement added, like saving commonly used references
    instead of calculating them each time.

Fix builds API response that did not include commit data

## What does this MR do?

This is fix for problem with builds API response not including information about commit this build is created for.

## What are the relevant issue numbers?

Closes #18476 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support 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 !4827

* upstream/master: (353 commits)
  Put some admin settings in dropdown
  Add styleguide on configuration settings documentation
  Remove Duplicated keys add UNIQUE index to fingerprint
  Avoid autoload issue such as 'Mail::Parsers::AddressStruct'
  Move appearance settings as sub tab to application settings
  use rails root join
  fixed a couple of errors spotted in production
  Fix RangeError exceptions when referring to issues or merge requests outside of max database values
  Fix bug in `WikiLinkFilter`.
  Grammar and typographic changes to artifacts documentation
  Tweak grammar
  Small frontend code fixes and restore 8a2d88f commit
  Warn about admin privilege to disable GitHub Webhooks
  Listing GH Webhooks doesn't stop import process for non GH admin users
  fixup! updated docs for api endpoint award emoji
  Update CHANGELOG
  Ensure Todos counters doesn't count Todos for projects pending delete
  Add endpoints for award emoji on notes
  Sort API endpoints and implement feedback
  Add endpoints for Award Emoji
  ...

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4093#note_12563922

For clarification and consistency

This is to ensure we don't send unwanted notifications when deleting a
project. In other words, stop abusing AR callbacks and use services.

Signed-off-by: Rémy Coutable <remy@rymai.me>