Capture `request.url` for Next.js server spans

[mydea]

Description

Today, the Next.js SDK in many cases captures only headers as event.request data, e.g. like this:

sentry-javascript/packages/nextjs/src/common/wrapGenerationFunctionWithSentry.ts

Line 70 in 56137a8

isolationScope.setSDKProcessingMetadata({

This leads to the url being missing context when looking at issues. We should investigate if we can find a way to add the url there, somehow - this probably involves injecting the url at some earlier point into async local storage so we can pick it up in our handlers, or something like this...