Issue #3615946: Detect any URL change instead of only native input events

Clear stale entity metadata (data-entity-type/uuid/substitution) whenever the link's href differs from linkCommand.value at execute time, rather than only reacting to a native 'input' DOM event on the URL field. A native 'input' event never fires when something else sets the field's value programmatically, e.g. CKEditor 5's core Bookmark feature (a 'link provider') writing an in-page fragment href directly into the field. Comparing against linkCommand.value also avoids relying on a value snapshotted earlier from the form, which is unreliable across the link balloon's visible view changing more than once (e.g. opening and closing a link provider's list).

Related to #3615946