Rework how shr sets <span id='foo'> targets to make it more reliable

Rework how shr sets <span id='foo'> targets to make it more reliable

* lisp/net/eww.el (eww-display-html): The target is now a list.
* lisp/net/shr.el (shr--link-targets): New variable.
(shr-insert-document): Set the targets.
(shr-descend): Save targets and apply them later.
(shr-ensure-paragraph): Remove hack to avoid filling from removing
targets.
(shr-tag-a): Save targets for later.
(shr-render-td-1): Bind and set targets (bug#52512).