Merge #4222

Merge #4222

4222: Introduce C/C++ for Visual Studio Code extension as an alternative debug engine for Debug Code lens. r=matklad a=vsrs

At the moment Debug Code Lens can use only one debug engine: lldb via [CodeLLDB](https://marketplace.visualstudio.com/items?itemName=vadimcn.vscode-lldb) extension.

This PR adds support of the debug engine from the [MS C++ tools](https://marketplace.visualstudio.com/items?itemName=ms-vscode.cpptools) extension, as well as the configuration option. If both extensions are installed, `CodeLLDB` will be used by default.

Another new option `rust-analyzer.debug.sourceFileMap` allows, for example, to step into Rust std library during debugging. Works only with `MS C++ tools`.

On Windows:
```json
"rust-analyzer.debug.sourceFileMap": {
    "/rustc/4fb7144ed159f94491249e86d5bbd033b5d60550": "${env:USERPROFILE}/.rustup/toolchains/stable-x86_64-pc-windows-msvc/lib/rustlib/src/rust"
}
```
On Linux:
```json
"rust-analyzer.debug.sourceFileMap": {
    "/rustc/4fb7144ed159f94491249e86d5bbd033b5d60550": "~/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust"
}
```

Co-authored-by: vsrs <vit@conrlab.com>