GraphQL query support for ezxmltext field type

[dfritschy]

Question	Answer
JIRA issue	none
Type	Feature
Target version	latest stable 1.9
BC breaks	no
Doc needed	no

This PR provides full GraphQL query support for ezxmltext field types.

Modelled after the richtext field type, it offers these subtypes:

  text:
        type: "String"
        description: "String representation of the value"
    xml:
        type: "String"
        description: "The raw ezxmltext xml"
    plaintext:
        type: "String"
        description: "Plain text representation of the value, without tags. Warning: the text representation may not be perfect."
    html5:
        type: "String"
        description: "HTML5 representation."

Note: mutations are not in the scope of this PR and are not a planned feature.

[bdunogier]

Looks good to me, besides the remark on the setting.

[dfritschy]

@bdunogier I have addressed your change request.

[vidarl]

Looks good to me.
@bdunogier : Can you confirm your initial remark is resolved

[dfritschy]

@bdunogier any reason not to approve and merge this PR?

[andrerom]

@dfritschy Could you rebase the work on latests 1.9 so we can verify that the tests passes?

[dfritschy]

@andrerom Rebased the pull request on latest 1.9, see no connection of the failing tests with my code

[bdunogier]

All good from my side, thank you @dfritschy !

[andrerom]

@dfritschy Sorry, but the failure seems to be relevant:

Exception: Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException: The service "ezxmltext.graphql.resolver" has a dependency on a non-existent service "ezpublish.fieldType.ezxmltext.converter.html5". in /home/travis/build/ezsystems/ezplatform-xmltext-fieldtype/vendor/symfony/symfony/src/Symfony/Component/DependencyInjection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php:31