Spawn cargo add in the new command

[tomasol]

Fixes #204
cargo component add now spawns cargo add cargo-component-bindings . This has a few implications:

• It makes the command a bit slower as it needs to fetch the metadata from the network
• It uses the latest version by default.
• When in a workspace, and cargo-component-bindings is already defined as a workspace dependency, it uses the workspace version.

cargo component upgrade was not changed. I believe this command does too much and should be reconsidered.

Tests did not have to be changed, but checking a specific cargo-component-bindings version in tests might be problematic.

[peterhuene]

Hi @tomasol. Thanks again for tackling this issue!

If we merge #212, the bindings crate has been removed entirely; however, it adds a dependency on wit-bindgen to pull in the runtime functions (disables the macro generation code, so it only has one additional transitive dependency).

So I think we should keep this change but update it for adding the dependency on wit-bindgen with --no-default-features and --features realloc.

That way we can remove the hardcoded version added by #212 and automatically pull it from a workspace if it's already there.

[peterhuene]

I've pushed up the proposed change and fixed a bug where we weren't checking the returned status for a non-successful exit (the workspace related tests should have failed as it wasn't adding the dependency because the workspace was setup before the subprojects were created; just had to fix the ordering in the tests).

[peterhuene]

@tomasol thanks again for the fix!

[tomasol]

@peterhuene Thanks for improving and merging the PR!