Speed up TypeScript Loader

[viferga]

The recent reimplementation of @trgwii of ts_loader has been a big improvement, but I think we can do it better. Due to that, I am going to open a new discussion here to talk about it.

Recently I found that ts-node implements skip of type-checking. Maybe we can learn from them and try to implement that in MetaCall. It can be enabled on an optional flag in the global configuration, but we can avoid type checking by default. All if this if avoiding this type-check phase still lets us introspect the type information.

The transpileOnly option implements this feature:
https://github.com/TypeStrong/ts-node/blob/bf470684a3a51f3900258d29306bf8227abd715f/src/index.ts#L327

Here is the if that branches depending on the flag:
https://github.com/TypeStrong/ts-node/blob/bf470684a3a51f3900258d29306bf8227abd715f/src/index.ts#L778

And here's the else part that is executed when transpileOnly is enabled:
https://github.com/TypeStrong/ts-node/blob/bf470684a3a51f3900258d29306bf8227abd715f/src/index.ts#L1150