According to
https://www.typescriptlang.org/docs/handbook/module-resolution.html#base-url,
`baseUrl` affects all non-relative imports. Additional `paths` mapping
can be specified for more control. However, if none of the `paths`
matches, it still falls back to the default `*:*` mapping. Confirmed by
invoking `tsc` with different configs.
Fixes#22663.