function withExtensions(elt, toDo) {
    forEach(getExtensions(elt), function(extension) {
      try {
        toDo(extension)
      } catch (e) {
        logError(e)
      }
    })
  }
`withExtensions` locates all active extensions for a provided element, then
executes the provided function using each of the active extensions.  It should
be called internally at every extendable execution point in htmx.

@param {Element} elt
@param {(extension:HtmxExtension) => void} toDo
@returns void