[6.1] Migrate from ESLint to Biome

[C-Lodder]

Summary of Changes

This migrates linting from ESLint to Biome, for 2 simple reasons:

1. Performance - Biome is at least 15x faster than ESLint due to the fact it's written in Rust and it multi-threadded.
2. Less dependencies - ESLint requires multiple plugins to work with languages and frameworks/libraries, whereas Biome supports them out of the box.

As part of this PR, I've also run the built-in formatter to try and use concise coding standards across the board.

@Fedik @dgrammatiko Would be nice to get your thoughts

[laoneo]

Did you add a line length? Would probably make sense to increase it, to have less changes in this pr.

[C-Lodder]

@laoneo The default is 80, which I believe is the same as ESLint.

Happy to increase this if you'd like a specific value, although 80 is generally considered a good number.

[laoneo]

If I remember correctly we were going in the past with 150. But can't find any evidence right now. Perhaps @wilsonge can shed some light here. Personally, I find 80 to close.

[laoneo]

These here are definitely incorrect.

[C-Lodder]

@laoneo Biome doesn't support .scss files, only .css, so shall I re-add the stylelint to cater for them?

[laoneo]

Looks like then, otherwise there is a better alternative.

[laoneo]

There is still an issue with the line length, changes like this one look wrong to me.

[C-Lodder]

@laoneo It wraps on a new line due to the default 80 character limit per line.

[C-Lodder]

I've just realised that eslint isn't even being properly used. All rules were removed in (#45784) other than no-restricted-globals,

[laoneo]

Nice. JS and vue files do look much better now.

[Bodge-IT]

Thanks for the work on this everyone. Just a little additional push to get this over the line is needed. Moved to 6.1 as 6.0 only in bugfix mode.