Show warning when loading a config in v3 fails

[thecrypticace]

Closes #1124

When IntelliSense loads a config file in v3, if that loading fails, it won't work at all even if your project is an otherwise valid project. There's also no indication to the user that this is the cause of IntelliSense not working.

This PR does two things:

• Uses the default config if loading the user's config does not work so you're likely to get IntelliSense for at least some utilities.
• Detects an issue when loading the config file and surfaces a warning to the user

Now, when given this config file:

import plugin from "i-do-not-exist";

/** @type {import('tailwindcss').Config} */
export default {
  content: ["index.html", "./src/**/*.{js,ts,jsx,tsx}"],
  theme: {
    extend: {
      colors: {
        primary: "orange",
      },
    },
  },
  plugins: [plugin],
};

You'll see a warning like this:

And IntelliSense will work for any default values (note how text-primary doesn't show a color swatch):

[philipp-spiess]

Nice!