Paths with dynamic routing params still not case-sensitive

[tsvetta]

Bug report

Describe the bug

The part of URL that goes after dynamic param (like [slug]) are still not case-sensitive.

To Reproduce

1. Create an empty next app
2. Create a page with dynamic parameter like: pages/dynamic/[slug]/route.js
3. Try to go to a route with upper-case letters like /dynamic/hello-there/RoUtE
4. The same page will be loaded as in the route /dynamic/hello-there/route

Also, I forked this repo and tried to write some tests, you can look at them here: #15394

I will be happy to read any advices.

Expected behavior

The part of the url that goes after dynamic param should also be case-sensitive and should send 404 page when try to load it.

System information

• OS: [e.g. macOS, Windows]
• Browser: chrome
• Version of Next.js: v9.4.5-canary.42
• Version of Node.js: 10.16.3

Additional context

Relates to #8848

[balazsorban44]

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