refactor bin entrypoint, add stackblitz support

[FredKSchott]

Changes

• resolves (hopefully) Setting up Astro with Stackblitz stackblitz/webcontainer-core#281
• improves our ESM support check to run in all environments

Testing

• Covered by existing tests
• Tested manually on Node 14.x, 12.10, 12.22, and 10.x

Docs

• Not needed

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astro-www – ./www

🔍 Inspect: https://vercel.com/pikapkg/astro-www/CkeS3RZVHMFEwKGBBMB5ohuXEoZH
✅ Preview: https://astro-www-git-stackblitz-support-pikapkg.vercel.app

astro-docs – ./docs

🔍 Inspect: https://vercel.com/pikapkg/astro-docs/89qwmByztpHcHyyrmDLgJkzU2H1H
✅ Preview: https://astro-docs-git-stackblitz-support-pikapkg.vercel.app

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Latest commit: a80a39c

The changes in this PR will be included in the next version bump.

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[aFuzzyBear]

Hi Fred, am I right in presumming that this fix needs to be waited for on stackblitz before it works? or should this work from now on? really happy that you have managed to take over and have this seen to completion, I think this would be brilliant for demonstrating the examples repo's

[FredKSchott]

Once this is released, stackblitz should at least run! There might be other bugs though so no promises that it will run successfully, but this solves the first blocker that we were running into.

[matthewp]

lgtm