Performance: replace field_read_instances() with field_info_instances()

Problem/Motivation

Currently the ctools relationship plugin (field_collection_field_collection_from_field_get_children()) uses field_read_instances() to determine the child plugins.
Unfortunately this function doesn't have a cache and since we use it in a pretty simple way we could fetch the same data using field_info_instances() which uses a cache if possible.

Proposed resolution

Change the processing to be able to use field_info_instances().

This also adds bundle independent plugins as proposed here: #2348995: Provide bundle independent ctools relationship plugin →

Remaining tasks

Reviews needed.

User interface changes

None.

API changes

I've seen that the bundle independent plugin definitions still use the context_name of the first bundle specific plugin. Because of the switch to field_info_instances() the processing order of bundles might changes, leading to a different context_name for bundle independent plugin definitions.
However, using the same context name for bundle specific and bundle independent plugin definitions seems odd anyway. So I guess if something should be fixed it's the generation of the context name of bundle independent plugin definitions and not the processing order.

Data model changes

None.