Relies on logic added to silverstripe/admin, so we need to bump the
constraint as well.
Behat test requires new logic added to the behat-extension module.
Anchors can come from additional WYSIWYG fields included inside
associated DataObjects. Don't assume all anchor links on the page are in
this one field.
When editing a page an author may insert anchors into their content (via
TinyMCE), and wish to link to those anchors from another point in that
page. E.g. creating a table of contents, a "jump to top" link at the
base of the content, etc.
Previously this required the page to first be saved as a draft, then
reloaded before the anchors would show in the list to link to. Now they
are dynamically pulled from the content entered for a more fluid editing
experience.
