As a result of reviews of the implementation of the EZP-28276 we now have \eZ\Publish\API\Repository\Values\Content\Field::$typeIdentifier property on API's Content Field Value Object.

Changing naming convention for \eZ\Publish\API\Repository\Values\ContentType\FieldDefinition::$fieldTypeIdentifier proven to be quite complicated, risky and without full confidence it is the right approach (see declined PR and explanation in alternative simpler PR).

The new idea is to change
\eZ\Publish\API\Repository\Values\Content\Field::$typeIdentifier
to
\eZ\Publish\API\Repository\Values\Content\Field::$fieldTypeIdentifier.