Mercury Editor libraries are attached to entity edit forms even when Mercury is not enabled for them

Problem/Motivation

Currently Mercury Editor's libraries are added via hook_library_info_alter(), which does not differentiate whether or not Mercury is enabled for an entity type. Issues like 🐛 Entity browser modals won't close on content types where Mercury is not enabled Active have occurred where JavaScript breaks on non-Mercury entity types.

Proposed resolution

Modify the way that Mercury Editor libraries are attached, such that they are attached only if Mercury Editor is enabled for an entity type. Otherwise, do not attach Mercury libraries and allow the default functionality to occur.