PHP 7.3 comes with the newer PCRE2 engine that is slightly stricter,
more specifically about using unescaped "-" within classes. They
now hat to be at the end of the class or escaped.
This is the only case we have found in core to make it compatible.
Also note that the file changes is, apparently an imported library,
but we have not it registered and already have performed changes to
it, so I've ignored that point. In fact, it has tabs and so on, I've
not modified that either.
- if the same image occurs several times on the page list it only once
- resolve image path correctly if it has a query string
- show images included in CSS
- non-JS file picker ignores thumbnail width and height attributes (this is a temp fix until renderers are implemented)