Track media usage and present it to the site builder (in the media library, media view, on media deletion confirmation, etc.)

Problem/Motivation

In addition to listing files, the core file view also lists and links usages. Another difference between the two views is that media may be deleted from the media view, whereas the files may be marked for deletion based on automatic (but broken) usage tracking.

User stories:

• As a media manager, I want to see where my media is used across the site (in entity relationship fields or in WYSIWYGs) so that I can effectively manage my media library and related content.
• As a media manager, I want to be prompted when I try to delete a piece of media that's in use (in entity relationship fields or in WYSIWYGs) so that I don't inadvertently break content or designs.

Proposed resolution

Add (non-broken) information on media usage and present it to the site builder where appropriate (on the media view / media library, possibly on the media deletion confirmation form, etc.).

Remaining tasks

Postponed on 🌱 Dealing with unexpected file deletion due to incorrect file usage Active .

User interface changes

API changes

Data model changes