make buildifier warning less aggressive

[jab]

trafficstars

This extension's warning about no buildifier being found is overly eager, and presumes that the environment should have a single, global buildifier executable shared by multiple projects.

But developers often prefer to have project-local versions of their tool dependencies (and no global version) for better reproducibility, which is even facilitated for buildifier by https://github.com/keith/buildifier-prebuilt. Note that all projects created via aspect init use this setup (see https://github.com/aspect-build/aspect-workflows-template).

Such users can add something like the following to ensure that a buildifier binary is available when their projects are opened and that the Bazel extension is configured to use it: .vscode/tasks.json:

    {
      // Build `buildifier` on folderOpen to ensure that a buildifier binary exists which the
      // VSCode Bazel plugin can use.
      "label": "Build buildifier",
      "command": "bazel build @buildifier_prebuilt//:buildifier",
      "presentation": {
        "reveal": "never",
        "panel": "new"
      },
      "runOptions": {
        "runOn": "folderOpen",
      },
      "type": "shell",
    }

.vscode/settings.json:

{
    "bazel.buildifierExecutable": "bazel-bin/external/buildifier_prebuilt~/buildifier/buildifier",
}

But even with this configuration, this extension still nags about no buildifier being found, because the check for it completes a split second before it's finished building, and it's never checked for again.

If the initial check fails, how about doing a retry or two with a sensible backoff?

cc @alexeagle