Composer: remove unused requirements, replace doctrine/common by doctrine/collections, declare the packages used directly #149

Description

Same cleanup as cleverage/process-bundle#268 (PR cleverage/process-bundle#281): some composer.json requirements are not used by the bundle but are forced on every application using it, and some packages used directly are only installed transitively (best practices for reusable bundles).

Checked on main @ d664410 (v3.2), in src/, config/, templates/ and tests/.

1. Unused requirements

2. Wrong package: doctrine/common instead of doctrine/collections

The only Doctrine\Common\* usage is Doctrine\Common\Collections\ArrayCollection (DoctrineProcessHandler), which belongs to doctrine/collections, not to doctrine/common.

3. Packages used directly but only installed transitively

Monolog (also used directly, only installed through cleverage/process-bundle) is handled separately in #150, as it is a prerequisite of cleverage/process-bundle#269.

The other requirements are used (e.g. symfony/expression-language by Assert\When, see #125; symfony/doctrine-messenger for the doctrine://default transport prepended by the extension; symfony/notifier stays optional: suggest + require-dev, guarded by interface_exists()).

Proposed fix

• Remove symfony/dotenv, symfony/runtime, ext-ctype and ext-iconv from require, and symfony/runtime from config.allow-plugins (unless the test setup needs them, then move them to require-dev).
• Replace doctrine/common by doctrine/collections (^2.2 || ^3, the range of doctrine/orm).
• Require the packages of table 3, with the lower bounds already imposed by their current providers (e.g. twig/twig ^3.24 || ^4, doctrine/persistence ^3.3.1 || ^4, doctrine/migrations ^3.2, psr/log ^1 || ^2 || ^3, symfony/event-dispatcher-contracts ^3, Symfony packages ^6.4 || ^7.4 || ^8).
• CHANGELOG entry noting that applications must require symfony/dotenv / symfony/runtime themselves (the Symfony skeleton already does).

Note: once both process-bundle (#281) and this bundle are released without symfony/dotenv / symfony/runtime, an application that does not require them itself loses vendor/autoload_runtime.php (bin/console, public/index.php) and Dotenv. The demo requires them since cleverage/process-bundle-demo#81 (PR cleverage/process-bundle-demo#82).

Requirements

• Documentation updates
  • Reference
  • Cookbooks
  • Changelog
• Unit tests

Breaking changes

None for the bundle API. Minor: applications relying on the bundle to install symfony/dotenv or symfony/runtime transitively must require them.