Allowed files for relative paths

[carlocorradini]

We already have a set of accepted files for non-relative paths introduced in version v3.8.
Introduce the allowlist for relative paths.
Consider the test multipleTsconfigs, where the only acceptable files in tsconfig.json are files": ["index.ts", "tsImportee.ts", "tsxImportee.tsx"]. However, in index.ts, we include two extra files (by relative pattern) from the subfolder directory that are not present in tsconfig.json.
Currently, this is accepted because it is a relative pattern and can be easily resolved, but I believe it should be reported because it is not explicitly available in the tsconfig.json.

What do you think? Should the inclusion be forced into tsconfig.json, or should the current practice be maintained?