Upgrade TypeScript to 3.3

[toolness]

This fixes #438.

Notes

• We work around Unexpected error when using generic with Pick and Exclude microsoft/TypeScript#28748 by using the fix described in Unexpected error when using generic with Pick and Exclude microsoft/TypeScript#28748 (comment). At first I got the heebie-jeebies when I saw props as any but as the OP says, we keep all the type checking on the outside, so type safety is maintained where it matters most. I've also left a note about this fix in all the places it's applied so that hopefully we can remove the workaround at some point when the issue is fixed.

• TypeScript 3.2's new support for Function.prototype.apply meant tweaking some typings where we used it.

• Apparently we were using the wrong behavior value for a ScrollBehavior but we should manually make sure nothing's broken.

To do

• Manually kick the tires, especially on IE 11, to make sure that the non-typing changes didn't break anything here (and to ensure that upgrading the TS compiler didn't break anything too, I guess).