Support for separate .cargo/config.toml files in different projects in a workspace.

[ryankopf]

The problem is if you have a workspace with subprojects that have different targets, they are not handled separately.

I created a reposity demonstrating the problem - https://github.com/ryankopf/testconfig

This is a problem because if you have a project, such as a video game, where you have two different targets (in my case one is wasm and one is linux/windows), Rust-Analyzer will die when it encounters a "compile_error!" macro in one of the projects, because the .cargo/config.toml file is not read for that project, and so Rust-Analyzer is not appropriately including the proper target in its checks.

This may be related to this issue - #13529 - but I think support for config.toml files is a separate issue that should be included.