Support elm-test-rs

[aszenz]

When elm-test-rs is installed i still get a pop up elm-test is not installed

Expected Behavior

When elm-test-rs is installed, elm-language server should use it instead of elm-test

Current Behavior

When elm-test-rs is installed via elm-tooling, it is present in node_modules/.bin/elm-test-rs, but elm-language-server doesn't use it, throwing pop up elm-test not found.

Possible Solution

The user can change the path of elm-test to point to elm-test-rs, but a nicer solution would be to support elm-test-rs as well

Steps to Reproduce (for bugs)

1. Clone the repo https://gitlab.com/exosphere/exosphere
2. npm install
3. Open any .elm file inside vscode, save and see the pop up about missing elm-test

Context

Since elm-tooling only lists elm-test-rs now for testing, i couldn't install elm-test, I expected elm-language-server to support elm-test-rs too.

Your Environment

• Version used: v2.6.0
• Editor used: vscode
• Environment name and version (e.g. node.js 5.4): 16.18.1
• Operating System and version: NixOS unstable