Support React Router v7 (library)

### Description

We want to support instrumenting React Router v7 (library): https://reactrouter.com/start/library/installation

This ticket is only about supporting React Router v7 as a routing library in a SPA. The upgrade from v6 is non-breaking.

- [x] sdk (https://github.com/getsentry/sentry-javascript/pull/14513)
- [x] docs (https://github.com/getsentry/sentry-docs/pull/11990)