Focus indicator is missing on nuxeo-document-grid-thumbnail

Fix issue described below as an example
See spreadsheet linked in epic for all references

Description
The visual focus indicator is missing altogether.

Elements:
Asset links in each grid cell

Note: The elements can be navigated through a keyboard using arrow keys.

The problem that it causes:
Sighted keyboard users will have no idea which link or control has focus making it extremely difficult, if not impossible, to interact with the content.