VScode extension: Install cargo-concordium through crates

[limemloh]

Description
Currently, the VSCode extension ships with binaries of cargo-concordium for every platform, meaning the current process is to first build cargo-concordium for every platform and then a vscode extension for every platform.
This made sense back when cargo-concordium was not released to crates.io, and now that it is, we could have the extension install it through this platform.

This will eliminate the need for platform specific builds of both cargo-concordium and the vscode extension.

[abizjak]

I think this is not a good idea. It's rather expensive to install it from source. It'd be worse user experience to do this.