build: fix tsconfig monorepo setup (#10028)

Should fix messed up import suggestions and simplifies all tsconfigs
through inheritance.

One main issue was that packages were inheriting `baseURL: "."` from the
root tsconfig. This caused incorrect import suggestions that start with
"packages/...".

This PR ensures that packages do not inherit this baseURL: "." property,
while ensuring the root, non-inherited tsconfig still keeps it to get
tests to work (the importMap needs it)

test/next-env.d.ts

@@ -2,4 +2,4 @@
 /// <reference types="next/image-types/global" />
 
 // NOTE: This file should not be edited
-// see https://nextjs.org/docs/basic-features/typescript for more information.
+// see https://nextjs.org/docs/app/building-your-application/configuring/typescript for more information.