Error missing information for Manually Edited Tags with multiple bad attributes

Problem/Motivation

When configuring a text format, and adding items to the "Source Editing" "Manually editable HTML tags" entry, if a tag has more than one bad attribute it doesn't display properly in the error.

Steps to reproduce

Create a basic content type, set "Manually editable HTML tags" to something redundant with existing settings (in my case I used <img id data-align lang>

Expected result:

Error message
The following attribute(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: <img id data-caption>.

Actual result:

Error message
The following attribute(s) are already supported by enabled plugins and should not be added to the Source Editing "Manually editable HTML tags" field: .

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet