refactor(es/typescript): Extract type annotation proposal out

[kdy1]

Description:

The Node.js team wants a Wasm package that only implements type annotation proposals. So we need to refactor our TypeScript transform to allow it.

Related issue:

• Support typescript with --experimental-strip-types  nodejs/loaders#208 (comment)

[kdy1]

@magic-akari Can you take a look? I looked at the TypeScript transform source code, but I'm not sure if applying StripType::default() is enough.

[magic-akari]

What I would like is for some option or collection of options where I can use SWC to implement the Type Annotations proposal, but nothing more. In particular, see https://github.com/tc39/proposal-type-annotations#intentional-omissions:

Originally posted by @GeoffreyBooth in nodejs/loaders#208 (comment)

Based on this requirement, I believe we only need to export StripType. What do you think? @kdy1

[kdy1]

I was thinking the same. I'll add a function for it.

[kdy1]

Thank you!

[kdy1]

swc-bump:

• swc_ecma_transforms_typescript
• swc_core

[magic-akari]

When using only StripType::default(), the following occurs:

• Enums and namespaces are disregarded and remain in place. (Previously handled by Transform)
• Implicit type imports are ignored; only syntactic type imports are processed by StripType. (Previously handled by StripImportExport)
• Declarations such as import foo = require('foo') and export = foo are left unprocessed. (Previously handled by Transform)
• Class constructor parameter properties are also left unprocessed. (Previously handled by Transform)

Are we on the same page? CC @GeoffreyBooth