Upcast deprecated table border attribute

The demo is split into three columns:

1. Editor
2. Source data (user agent styles)
3. Source data wrapped in the .ck-content class

Each table has the deprecated border attribute set to 10 (except those which are marked as 0-border tables), along with additional inline styles that affect how the table border is rendered.

By default, CKEditor 5 applies a double border style to tables and sets border-collapse to collapse.