Link field doesn't work as mapping source & target

Problem/Motivation

If the entity to be imported has a Link field (with separate URL & Title) the Feeds Type Mapping will allow you to choose 2 separate sources, but if you select a Link field defined on the Feeds Type (so the user creating the feed will be able to set the link on all imported items), and you select the same field twice (since you can't select URL & Title parts of a Link field separately), the import will fail.

Proposed resolution

Show & allow selecting the Link field URI and Title text separately in the Mapping sources.

These past issues related to Link fields may be useful (they're all about 7.x-2.x version):

1. #1345570: Link url mapping not working →
2. #1181092: Link Mapper field name problem - Title overwrites url →
3. #1182462: Link mapper does not set a real_target →

Remaining tasks

User interface changes

API changes

Data model changes