BUGFIX: Always run composer from Flow root path

[eWert-Online]

This bugfix ensures, that the composer require command always gets executed in the Flow root path (by calling composer require with the --working-direcory flag set to FLOW_PATH_ROOT .)

It also introduces the composer/composer package to the codebase to replace the exec command.

Fixes #1832
Fixes #1778

[kdambekalns]

From the original PR description:

How to verify it

1. run the kickstart:site command from any other direcory than the Flow root path
   (ex: ./test/flow kickstart:site Package.Name test)
2. create a site-package with the web setup tool.

Note
I did close and reopen the pull request, because i branched off from master and not from 5.2
Sorry for the inconvenience

[mficzel]

I like this approach but i run into trouble when running
./flow package:create --package-key Foo.Baz

Result:

Class 'Composer\Console\Application' not found
  Type: Error
  File: Packages/Framework/Neos.Flow/Classes/Package/PackageManager.php
  Line: 394

I added the repo to the composer.json and ran composer update which lead to composer/composer be installed but some weird info messages are shown.

Seems i had composer issues, will add a proper review now

[mficzel]

I like this change and can confirm that it works. Should have been like this in the first place.

@kdambekalns can you verify that the composer/composer dependency is introduced in a way that works with the subsplits.

[kdambekalns]

Will do…

[kdambekalns]

From looking at it it seems perfect. The dependency is declared with neos/flow itself and the collection manifest has been updated. That should not interfere with anything split-related.

I just wonder why we ever had Flow depend on itself as a dev-dependency… 🤷‍♂️

[kitsunet]

This is great, but also shows that now Flow will depend on composer, I guess we should move package creation out of the package manager ASAP and into the flow/kickstarter so you can get rid of that and the composer requirement when you want to. Alas not related to this change which definitely brings things in the right direction.

[kdambekalns]

shows that now Flow will depend on composer

Isn't that an opportunity? I am quite sure we have some dependency-order code that we could delegate, no?

[kitsunet]

Hahaha, good idea, will have to look into that and see if we could actually do that to order packages for settings and such.