PHPStan: Add support for multiline messages

[greg0ire]

When using PHPStan, you might get multiline messages in some cases:

/home/greg/dev/doctrine-migrations/tests/Doctrine/Migrations/Tests/Metadata/Storage/ExistingTableMetadataStorageTest.php:83:Fetching class constant class of deprecated class Doctrine\DBAL\Connections\MasterSlaveConnection:
Use PrimaryReadReplicaConnection instead
/home/greg/dev/doctrine-migrations/tests/Doctrine/Migrations/Tests/Metadata/Storage/TableMetadataStorageTest.php:200:Instantiation of deprecated class Doctrine\DBAL\Driver\PDOSqlite\Driver:
Use {@link PDO\SQLite\Driver} instead.
/home/greg/dev/doctrine-migrations/tests/Doctrine/Migrations/Tests/Tools/Console/Command/StatusCommandTest.php:77:Call to method compare() of deprecated class Doctrine\DBAL\Version:
Refrain from checking the DBAL version at runtime.

Without this patch, the messages get truncated and you only get the first line, so just Instantiation of deprecated class Doctrine\DBAL\Driver\PDOSqlite\Driver:

With it, you can get the whole message. (Instantiation of deprecated class Doctrine\DBAL\Driver\PDOSqlite\Driver: Use {@link PDO\SQLite\Driver} instead.)

This is achieved by switching to JSON, which makes it much easier to
avoid confusion between an error message and the next one. It also
spares us from having to deal with regular expressions, and eliminates
some edge cases that no longer need to be tested.

[greg0ire]

ping @w0rp I've been using this for almost 2 months now, no issues 🙂

[hsanson]

Looks good to me and json output seems to have been supported for long time.