Shorten method signatures (aka "type madness")

Some of the types that make everything work behind the scenes are ridiculous. For example, from Vue.js:

For a Vue developer creating a new Vue instance in JavaScript, they will be exposed to this every time. If they already know what arguments to supply, this does not do a great job as a quick reminder. If they don't know what args to supply, this is probably not very helpful either. We should be able to give users an option to show a concise method signature like the following.

In this example, the tildas indicate that there is "type madness" hidden below. If the user really wants to see the types, they can goToDefinition or maybe we could give them a way to expand the signature window.

We would need to pick some arbitrary line when to display type information and when to hide it. My initial thinking is something along the lines of:

• Hide all generic types, but leave angle brackets in
• Hide types when there are more than 2 unions or intersections
• Show string literals if less than 100 characters (roughly 2 lines?)

I would imagine we would also want to give JavaScript users the concise signature by default and TypeScript users the full signature by default, but give both the camps the ability to configure to their preference.

The issue names no files, tests, or entry points. Start by reviewing the proposed rules for hiding generic types, unions, intersections, and long string literals, along with the requested JavaScript and TypeScript defaults; done means users can configure concise or full signatures and see the intended form.