Fix the Red Squigglies

[sylvanc]

Red squigglies now appear in a manner similar to Ionide.

Typechecking is done:

• When the notebook loads, AND
• When Intellisense is invoked, AND
• When the code has changed since the last type check, but nothing has changed for at least 1 second.

This gives delayed but constant typechecking.

[cgravill]

Excellent, this definitely reduced the false positive rate of red squiggles on a few cases I tried and makes for a better editing experience.

We are missing some errors that Ionide can project in e.g.

vs

I'd be happy for this to be merged as it gets right what it does in my interactions. Then later we can decide about covering more cases.

[sylvanc]

Hmm, wonder why it doesn't catch that! Merging, and we can improve it more :)