chore: use external xast type declarations

[SethFalco]

Removes our custom type declarations for Xast in favor of the ones suggested by xast.

If you are using TypeScript, you can use the xast types by installing them with npm:

npm install @types/xast

— https://github.com/syntax-tree/xast#types

Motivation

While it makes sense to declare types of Xast for our plugin API, I think it'd be better to avoid maintaining them as part of this library/application if there are conventional solutions available already.

• Imo it's better to leave maintaining/redistributing them to @DefinitelyTyped, which Titus Wormer and Christian Murphy from syntax/xast helped define.
• The new types more strictly adhere to the Xast spec, which should simplify integrating with Xast libraries in future.

My hope was actually to explore some libraries surrounding Xast, in particular, xast-util-from-xml and xast-util-select. Unfortunately, neither of these meet fulfil our needs atm.

---

Not sure if this is a worthwhile change, so feedback welcome.

[TrySound]

Working with attributes with these types is less trivial though parser produce only string values. I'd prefer to stay with old types.

This change also introduce 2 more packages. xast-util-from-xml would bring even more.
Last couple months I had very bad Internet connection and loading myriads of packages in node_modules made it worse. So I'd encourage you to keep svgo more concentrated.

Underlying xml parser seem interesting though. We could write own wrapper around it and replace sax.

[SethFalco]

Sounds good, I'll shelve this then!

Underlying xml parser seem interesting though.

Unfortunately, one thing that will stop us from using it for now is the lack of support for DTD entities.

https://github.com/rgrove/parse-xml#not-features

Not sure if that's planned, or something we'd be able to work around. I'll review both later, but right now, I'm more focused on documentation.

WIP:

[TrySound]

Awesome!

[TrySound]

Wrote to you in matrix