ref(nextjs): Move pages router instrumentation into separate folder

[lforst]

Simply moves all runtime agnostic instrumentation related to the pages router into its own folder.

[github-actions]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	22.73 KB	added	added
@sentry/browser - with treeshaking flags	21.53 KB	added	added
@sentry/browser (incl. Tracing)	34.97 KB	added	added
@sentry/browser (incl. Tracing, Replay)	71.5 KB	added	added
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	61.91 KB	added	added
@sentry/browser (incl. Tracing, Replay with Canvas)	75.82 KB	added	added
@sentry/browser (incl. Tracing, Replay, Feedback)	88.59 KB	added	added
@sentry/browser (incl. Tracing, Replay, Feedback, metrics)	90.46 KB	added	added
@sentry/browser (incl. metrics)	27 KB	added	added
@sentry/browser (incl. Feedback)	39.87 KB	added	added
@sentry/browser (incl. sendFeedback)	27.38 KB	added	added
@sentry/browser (incl. FeedbackAsync)	32.17 KB	added	added
@sentry/react	25.49 KB	added	added
@sentry/react (incl. Tracing)	37.94 KB	added	added
@sentry/vue	26.9 KB	added	added
@sentry/vue (incl. Tracing)	36.86 KB	added	added
@sentry/svelte	22.87 KB	added	added
CDN Bundle	24.05 KB	added	added
CDN Bundle (incl. Tracing)	36.76 KB	added	added
CDN Bundle (incl. Tracing, Replay)	71.24 KB	added	added
CDN Bundle (incl. Tracing, Replay, Feedback)	76.55 KB	added	added
CDN Bundle - uncompressed	70.53 KB	added	added
CDN Bundle (incl. Tracing) - uncompressed	109.04 KB	added	added
CDN Bundle (incl. Tracing, Replay) - uncompressed	220.93 KB	added	added
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	234.15 KB	added	added
@sentry/nextjs (client)	37.91 KB	added	added
@sentry/sveltekit (client)	35.56 KB	added	added
@sentry/node	125.03 KB	added	added
@sentry/node - without tracing	93.48 KB	added	added
@sentry/aws-serverless	103.17 KB	added	added