feat: introduce candid-extractor for candid export

[lwshang]

Description

SDK-1227

Rework the "Candid Export" support introduced in v0.10.

The new version needs no crate features in ic0 and ic-cdk-macros anymore.

And the canister can still invoke ic_cdk::export_candid!() at the end of source code.

Then candid-extractor can extract candid from the canister WASM (the same WASM module to be deployed on IC).

How Has This Been Tested?

Examples end-to-end tests.

Checklist:

• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[chenyan-dfinity]

Interesting idea! There are two approaches to solve the double compilation problem with different pros and cons:

1. As you proposed here, we can provide the ic imports in the wasmtime runtime.
2. We can build a Wasm transformation that takes out the ic imports, so that it can run with regular wasmtime.

For 1), we need a special wasmtime (candid_extractor in this case), and the output candid function will be in the deployed canisters.
For 2), we need a regular wasmtime, which can also be used for Motoko unit testing as well. The transformation can be useful in other cases, e.g., when some crates accidentally import some non-ic modules, we can help remove them.

[lwshang]

This is a intermediate stage of candid exporting epic. The candid_extractor CLI is a temporary component.
My next step is to integrate such specialized wasmtime into dfx. And add a config in dfx.json to let a canister opt in such candid export behavior.

As this will be built into dfx, developers won't need install other tools like wasmtime. And there will be only one WASM for both deploying and extracting candid.