Lumino 2 - meta PR with multiple items resolved

[afshin]

• Fixes Update to TypeScript 4.x #318
• Fixes Fix GlobalCompositeOperation error in data grid package #298
• Fixes Remove @lumino/datastore from Lumino 2 #320
• Removes deprecated CSS class names and icon APIs
• Removes deprecated mouse events from @lumino/dragdrop and @lumino/widgetsin favor of pointer events
• Removes es6-promise polyfill
• Removes simulate-event from the dependencies and uses native dispatchEvent and Event, FocusEvent, KeyboardEvent, MouseEvent, and PointerEvent
• Fixes a bunch of eslint issues that show up in GitHub
• Removes the crypto dependency in @lumino/coreutils because Node ships with a crypto module in its standard library

[bollwyvl]

It would be lovely if command schema happened in 2.

edit: see it's in the plan on #233 😊

The quesiton remains whether it ships with a validator.

[fcollonval]

Thanks a lot for this big clean up @afshin

I have minor questions but the new code is looking good.

[afshin]

Even though the RTD job doesn't fail, the rendered output actually looks broken.

I'm not sure how to fix it, but let's not merge this until the docs work.

[afshin]

I will stop adding to this PR because there's still plenty left to do and it will just get bigger and bigger. I added #325 to denote that the dependency updates are not yet finished.

[fcollonval]

Thanks @afshin

Let's merge this one.

[afshin]

Fixes #106