Package manager agnostic Tauri build scripts

[carlos-menezes]

Currently, Tauri's build scripts are not package-manager agnostic

"build": {
    "beforeDevCommand": "yarn dev",
    "beforeBuildCommand": "yarn build",
    "devPath": "http://localhost:1420",
    "distDir": "../dist",
    "withGlobalTauri": false
  }

There's one easy way to accomplish this, with the only downside being that the npm command will run if the yarn command fails (e.g. the build fails).

    "beforeDevCommand": "yarn dev || npm run dev",
    "beforeBuildCommand": "yarn build || npm run build",

Alternatively, we could substitute the yarn command by node $npm_execpath run <script> (on Unix systems) or node \"%npm_execpath%\" run <script> (on Windows). The only downside to this approach is that you would need dev.unix and dev.win: essentially, repeat every script twice.

Or just support yarn. What are your thoughts?