[Forwardport] Introduce Block Config Source

[thomas-kl1]

Original Pull Request

#16021

Add a new OptionSource of Blocks

Description

Pages config source is useful to create custom configuration, for example to set page. The same for the block could be useful too.
So I suggest to add the blocks config source.

[magento-engcom-team]

Hi @thomas-blackbird. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[osrecio]

Hi @thomas-blackbird ,Thanks for your contribution.

Can you check the error in Travis. ?

You should add declare(strict_types=1); for

app/code/Magento/Cms/Test/Unit/Model/Config/Source/BlockTest.php
app/code/Magento/Cms/Model/Config/Source/Block.php

You have mor information in Technical Guidelines

1.3.1. All new PHP files MUST have strict type mode enabled by starting with declare(strict_types=1);. All updated PHP files SHOULD have strict type mode enabled.

Thanks!

[thomas-kl1]

Intégration test has failed. I can't see how it can be related. Please advise,

[osrecio]

The error is not related eith your PR, I will process ASAP.

Thanks @thomas-blackbird

[magento-engcom-team]

Hi @thomas-blackbird. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.