Core htmx extension tests

• withExtensions catches and logs any exceptions0ms ‣

  htmx.defineExtension('ext-prevent-request', {
    onEvent: function(name, evt) {
      if (name === 'htmx:beforeRequest') {
        evt.preventDefault()
      }
    }
  })
  var div = make('<div hx-ext="ext-prevent-request">Foo</div>')
  htmx._('withExtensions')(div, function(extension) {
    throw new Error('throw error to catch and log')
  })