Enhancement: Allow creating ContainerBuilder with definitions for default extensions

[localheinz]

What is the reason for this PR?

• allows creating a ContainerBuilder with definitions for default extensions

Related to #719.

Author's checklist

• Follow the Contribution Guide

Summary of changes

Review checklist

• All checks have passed
• Changes are approved by maintainer

[localheinz]

This method can provide an extension point for people who want to

• add extensions
• override default extensions

<?php

declare(strict_types=1);

use Faker\Container;
use Faker\Extension;
use Faker\Generator;

require_once __DIR__ . '/../vendor/autoload.php';

$container = Container\ContainerBuilder::withDefaultExtensions()
    ->add(Extension\FileExtension::class, static function (): Extension\FileExtension {
        return new CustomFileExtension();
    })
    ->build();

$faker = new Generator($container);

This method is similar to the method simplified in #720, but returns the ContainerBuilder instead of the built Container.

[localheinz]

We can probably remove this method - I don't see any use for it (also see changes below).

[bram-pkg]

One conflict to resolve, @localheinz

Otherwise LGTM

[localheinz]

Thank you, @bram-pkg!