Add api.Document.selectstart_event (#3949)
Add api.Document.selectstart_event (#3949)

* Add api.Document.selectstart_event

* Set Chromium to false

* Set Chromium to true

* Mirror from api.GlobalEventHandlers

mdn/browser-compat-data,chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data