feat(wasm): add support for wasip2, aka webassembly components, using wasi-http

[brooksmtownsend]

Fixes #2294

Hey there! This is a work-in-progress PR that adds support for using reqwest with wasi-http. It was really neat to see the support for wasm_bindgen and JavaScript bindings for requests, and this PR helps support the component model in addition to wasm_bindgen.

I wanted to open this PR to see if you had any suggestions, requests from the initial working code/refactor perspective, and if there's any additional material you'd like me to clarify. If this fits within your general contribution guidelines, I'll wrap it up and mark as ready for review!

This code is still very littered with unwraps and comments, so go easy on me if you take a look at the implementation 😅 . To name a few, here's the things I want to do still for this PR:

• General code cleanliness, no doc comments simply added as dox, kill unwraps, expects, and panics
• Add example that I'm using for testing under the examples dir
• Gate wit-bindgen behind the wasm32 family of deps
• See if I can better toggle between the JS/bindgen Wasm support and the component model wasm support using directives instead of a feature (there is the wasm32-wasip2 target but that's not very widely used yet.) The goal here is to not affect any existing use cases of wasm -> reqwest and add support for components.
• Consider a custom pollable to remove the technically blocking code in the request

Last but not least, thanks for this library! Love reqwest ❤️

[seanmonstar]

Thanks for taking a look at this! I think support WASI is likely a good goal, in general. However, I usually try to have the discussion in an issue first. I find it's helpful to find consensus before spending too much time going down a certain implementation path, or even working on a feature that won't be accepted at all.

So while I do appreciate exploring the area, and exploration is often needed to inform more complex features, I do want to set proper expectations: we might not do this, or do it very differently. 🙈

[brooksmtownsend]

@seanmonstar that's why I opened the draft PR! Glad I ended up doing that before I got too far down the road. I can open up an issue then and point at this branch as a reference if that's what you prefer

[brooksmtownsend]

Oh fun, #1956 and #1977 exist. Do we need another issue? Looks like the implementation in #1956 is also an option for comparison, albeit not quite on wasi-http@0.2.0.

[brooksmtownsend]

Created #2294 to further the discussion, @seanmonstar please feel free to either close this PR for now while we continue in the issue or leave it open, totally up to the way you like to track the OSS work.

[brooksmtownsend]

Rebased this PR off of main and added a component example so folks can see this in action. With reqwest it is really nice looking