Views does not support computed bundle fields

Problem/Motivation

Since #2852067: Add support for rendering computed fields to the "field" views field handler Views can render computed fields. However, this only works for computed base fields not computed bundle fields.

The problem is that generally a view is not specific to a given bundle, so we cannot know up-front to which bundle a (computed) bundle field may belong.

Proposed resolution

Allow specifying a bundle key as part of the views data for (computed) bundle fields and - if it is - fetch the respective field definition for that bundle.