Switch to flat config

[fregante]

I'm opening this tracking issue to collect related tickets.

This change blocks:

• Suggestion on slimming down dependencies #2151
• npm audit security vulnerability in semver <= 7.5.2 #2163

[silverwind]

Does it have to be a "switch"? There are a number of plugins that support both configs at the same time and I think it would ease the migration.

[fregante]

I think the flat config is already supported:

• Support ESLint new config system #1886

So this issue is to drop support for the old config, essentially. It's not something that will happen anytime soon, I suppose.

[philsherry]

ESLint v8.x end of life was October 5, 2024, so Flat config is the only way forward now.