🥉 Minor codebase updates and fixes

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Congrats! I'm gonna use this issues as a placeholder for the next #5222 issue 😌

plz don't comment or add labels.

If you see this issue, you will have 56 years of good luck.

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• Show the username of the entered token (as part of the scope check UI)
• Fix some TODOs
• Use SearchQuery in most places where we build/alter search queries.

Examples: https://github.com/search?q=repo%3Arefined-github%2Frefined-github+%2Fis%3Aissue%2F&type=code

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• Use experiments.css in webpack: https://webpack.js.org/configuration/experiments/#experimentscss

CSS extraction: webpack will extract CSS into a separate file. This functionality replaces the need for mini-css-extract-plugin and css-loader, as it provides native support.

Blocked by:

• experiments.css is not equivalent to the mini-css-extract-plugin it's meant to replace webpack/webpack#17700

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• Correctly support URLs like https://github.com/refined-github/refined-github/assets/50487467/747b5133-61b8-490e-b961-4e5390ea9482 in the readme-parser and feature validator. Currently they're silently ignored

Seen in #6900 (review)

• Verify toggle-everything-with-alt and extract selectors into selectors.ts in order to test them with real URLs

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• Add waitForChildren to the selector observer

See sindresorhus/element-ready#29. Occasionally we need to ensure the full element has been loaded and we already have some workarounds for that, for example in #6909

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• Move Contributing.md to the wiki

https://github.com/refined-github/refined-github/blob/main/contributing.md