Update all constructors, including [HTMLConstructor]

This updates all the constructors in the standard for recent changes to
Web IDL. In particular:

* Replace [Constructor] extended attributes with constructor operations
* Cross-links constructor operations on events to the DOM event
  constructor definition
* Changes [HTMLConstructor] to apply to constructor operations, instead
  of to interfaces, and updates all usages of it
* Changes the definition of [HTMLConstructor] to leverage new Web IDL
  concepts of "usual constructor steps" and "internally create a new
  object implementing the interface"

Fixes #4870. Fixes #4890.