fix(router-vite-plugin): use cwd instead of vite.root

[a-maas]

fixes #1550.

Based on the issue, I was experiencing issues with the vite plugin generation not working when using a non-standard vite root configuration. This was caused by a mismatch between most of the code using ./ or process.cwd() as the relative root, and this line using vite.root.

I don't think vite's root config is strictly necessary here, because the TSR configuration already allows you to configure your routesDirectory and generatedRouteTree if using a non-standard directory structure.

[nx-cloud]

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