Upgrade Astro to version 3

[nickrttn]

Taking it one major at a time. This PR:

• upgrades Astro to v3 and Astro plugins to versions matching Astro v3.
• updates the config accordingly
• removes a script that was used when migrating from Jekyll to Astro and will never be used again
• sets the default formatter for Astro files to the VS Code Astro plugin
• removes remark-emoji, it was only used for two emojis. Instead, force emoji's to color emoji's using system-default color emoji font families where needed, or use Unicode emoji's.
  • this package also has mismatching types with the upgraded Astro, and so removing it was the easiest route considering it was already fairly heavy-handed for the two emoji's we were using it for.
• fixes linting errors that were the result of the upgrade (eg. adding is:inline to some script tags)

[Acconut]

Thank you very, very much for this PR!

[Acconut]

Should all emojis be wrapped in this element now?

[kvz]

Awesome Nick! Just a few minor questions about this

[kvz]

All good here! Can be merged as soon as the merge conflict is resolved imo

[Acconut]

Thank you very much, Nick!