add service definition for form field title extractor

[Guite]

This PR adds a service definition for the extractor wanted in #394

Do not merge before php-translation/extractor#148 is merged.

[odolbeau]

Version 2.0.1 of extractor released!
https://github.com/php-translation/extractor/releases/tag/2.0.1

[Guite]

what's the state of this PR? anything to do in order to get it merged?

[odolbeau]

Could you remove the non-trigerred PHPStan error & replace the service declaration with the code suggested by @rvanlaak please?

_instanceof:
    PhpParser\NodeVisitor:
        tags:
            - { name: 'php_translation.visitor', type: 'php' }

It will avoid the current Travis error when the bundle is used with a php-translation/extractor version which doesn't contain the new visitor.

It's done in #396 but this PR does several things. :/

[Guite]

@odolbeau done both but eventually this lead to including almost everything from #396 - except the autowire enablement.

[odolbeau]

@Guite could you squash your commits please?
@rvanlaak WDYT?
It it OK for you if we merge this PR which is now ready to be merged or do you prefer to correct #396?

[Guite]

could you squash your commits please?

Please do so when clicking on the merge button.