feat(browser): Record standalone LCP spans

[Lms24]

This PR implements sending standalone LCP spans as an opt-in feature.

Behaviour-wise, it's mostly aligned with our prior implementation of sending CLS standalone spans (#13056):

• add an _experiments.enableStandaloneLcpSpans option and treat it as opt-in
• keep collecting LCP values until users soft-navigate or the page is hidden
• then, send the LCP span once
• adds all lcp.* span attributes as well as the lcp measurement to the span

(depending on if we merge #16589 or this first, we might need to readjust size limit)

closes #13063

[github-actions[bot]]

size-limit report 📦

Path	Size	% Change	Change
@sentry/browser	23.99 kB	-	-
@sentry/browser - with treeshaking flags	23.76 kB	-	-
@sentry/browser (incl. Tracing)	39.02 kB	+0.47%	+179 B 🔺
@sentry/browser (incl. Tracing, Replay)	77.16 kB	+0.23%	+174 B 🔺
@sentry/browser (incl. Tracing, Replay) - with treeshaking flags	70.25 kB	+0.27%	+185 B 🔺
@sentry/browser (incl. Tracing, Replay with Canvas)	81.93 kB	+0.23%	+188 B 🔺
@sentry/browser (incl. Tracing, Replay, Feedback)	94.02 kB	+0.21%	+191 B 🔺
@sentry/browser (incl. Feedback)	40.75 kB	-	-
@sentry/browser (incl. sendFeedback)	28.7 kB	-	-
@sentry/browser (incl. FeedbackAsync)	33.59 kB	-	-
@sentry/react	25.76 kB	-	-
@sentry/react (incl. Tracing)	41 kB	+0.39%	+159 B 🔺
@sentry/vue	28.36 kB	-	-
@sentry/vue (incl. Tracing)	40.86 kB	+0.39%	+155 B 🔺
@sentry/svelte	24.01 kB	-	-
CDN Bundle	25.5 kB	-	-
CDN Bundle (incl. Tracing)	39.11 kB	+0.5%	+191 B 🔺
CDN Bundle (incl. Tracing, Replay)	75 kB	+0.23%	+168 B 🔺
CDN Bundle (incl. Tracing, Replay, Feedback)	80.46 kB	+0.21%	+162 B 🔺
CDN Bundle - uncompressed	74.5 kB	-	-
CDN Bundle (incl. Tracing) - uncompressed	116.63 kB	+1.05%	+1.21 kB 🔺
CDN Bundle (incl. Tracing, Replay) - uncompressed	230.68 kB	+0.53%	+1.21 kB 🔺
CDN Bundle (incl. Tracing, Replay, Feedback) - uncompressed	243.5 kB	+0.5%	+1.21 kB 🔺
@sentry/nextjs (client)	42.63 kB	+0.38%	+161 B 🔺
@sentry/sveltekit (client)	39.49 kB	+0.4%	+155 B 🔺
@sentry/node	154.29 kB	-	-
@sentry/node - without tracing	98.64 kB	-	-
@sentry/aws-serverless	124.4 kB	-	-

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