Slow type checking with snabbdom 3.6+

[Jonathan Gamble]

Recent releases after 3.5.1 seem to really trouble tsc.

We import and use snabbdom from ~ 31 modules of a monorepo.

Our type checking takes 3x as long when those modules import snabbdom 3.6 vs 3.5.1.

48s vs 14s

[Simon Friis Vindum]

Hi @schlawg. Thanks for reporting this. That is quite a noticeable slowdown. Would it be possible for you to git bisect this to figure out what caused the issue?

One thing I can think of regarding typing is that the types for JSX was improved in #1092.