make pageExtensions string array possible to negate values

[angelod1as]

Goals

1. Instead of passing the files that pageExtensions should consider as pages, we should be able to add negations — files we don't want to be expected as pages, e.g. pageExtensions: ["!.test.tsx"] or similar.
2. This way, instead of colocating and having to change all files to e.g. .page.tsx, we'd only exclude the said pages from pageExtension, making it cleaner and easier to maintain.

Non-Goals

1. We don't need a complicated glob or pattern matching. A simple "!" in front would be enough.

Background

I want to create test files besides my pages files and they are interpreted as pages. The docs tell me to add the .page.tsx suffix to every page, but this gets complicated when there are a lot of existing files in a constant changing environment.

Adding an exclusion to pageExtensions would make everything way easier, in a way I could just exclude the files that end with .test.tsx. Easy peasy.

Proposal

I don't know exactly how pageExtensions work and how it deals with empty values (default). I think it should take into account anything in the array, filtering out the negations. If there's only negations, it treats every file except the negated as valid.

I am interested in contributing.