Move from `tsconfig.json` paths to Subpath imports

[avivkeller]

(Self-assigning as I am happy to take this on)

Currently, we’re using TypeScript’s paths option to handle module imports (which, until recently, was enforced by our linter).

While this setup has worked, it’s created several ongoing hurdles:
• Packages can't import modules with the same selector
• Our test runner needs a TypeScript transpiler that supports these aliases, limiting our ability to adopt faster alternatives
• Extra overhead in maintaining consistency between tsconfig.json in various places

To simplify things, I propose we move to Node.js native import aliases. This would involve changing our current @ prefix to something like #, following the Node convention.

[AugustinMauroy]

The last time I tried it, it went wrong with Next.js. Do you know how to validate that it works?

[avivkeller]

Turborepo actually recommends it, but I'll do some testing.

[AugustinMauroy]

Nice !

[avivkeller]

See #7735