feat(browser): Warn on duplicate browserTracingIntegration

[mydea]

Closes #16040

this logs a warning if a user adds multiple instances of browserTracingIntegration. If this is done, this can lead to potentially weird things (e.g. we add multiple handlers etc).

This is especially relevant for react, as there are multiple different integrations there that users may add.

[github-actions]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	23.28 KB	-	-
@sentry/browser - with treeshaking flags	23.12 KB	-	-
@sentry/browser (incl. Tracing)	36.99 KB	+0.12%	+42 B 🔺
@sentry/browser (incl. Tracing, Replay)	74.17 KB	+0.04%	+30 B 🔺
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	67.55 KB	+0.06%	+41 B 🔺
@sentry/browser (incl. Tracing, Replay with Canvas)	78.83 KB	+0.05%	+34 B 🔺
@sentry/browser (incl. Tracing, Replay, Feedback)	90.65 KB	+0.05%	+45 B 🔺
@sentry/browser (incl. Feedback)	39.68 KB	-	-
@sentry/browser (incl. sendFeedback)	27.9 KB	-	-
@sentry/browser (incl. FeedbackAsync)	32.67 KB	-	-
@sentry/react	25.09 KB	-	-
@sentry/react (incl. Tracing)	38.91 KB	+0.12%	+44 B 🔺
@sentry/vue	27.51 KB	-	-
@sentry/vue (incl. Tracing)	38.71 KB	+0.1%	+39 B 🔺
@sentry/svelte	23.32 KB	-	-
CDN Bundle	24.51 KB	-	-
CDN Bundle (incl. Tracing)	36.98 KB	+0.1%	+37 B 🔺
CDN Bundle (incl. Tracing, Replay)	72.03 KB	+0.05%	+34 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback)	77.18 KB	+0.03%	+22 B 🔺
CDN Bundle - uncompressed	71.47 KB	-	-
CDN Bundle (incl. Tracing) - uncompressed	109.34 KB	+0.1%	+111 B 🔺
CDN Bundle (incl. Tracing, Replay) - uncompressed	220.63 KB	+0.05%	+111 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	233.16 KB	+0.05%	+111 B 🔺
@sentry/nextjs (client)	40.53 KB	+0.1%	+38 B 🔺
@sentry/sveltekit (client)	37.44 KB	+0.14%	+52 B 🔺
@sentry/node	143.23 KB	-	-
@sentry/node - without tracing	96.47 KB	-	-
@sentry/aws-serverless	120.77 KB	-	-

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