feat(sveltekit): Automatically add BrowserTracing integration

[Lms24]

With this PR, the BrowserTracing integration is automatically added to the client SvelteKit SDK initialization. As in NextJS, tree-shaking will still work by replacing the __SENTRY_TRACING__ flag with false when bundling. Tested this with the rollup replace plugin.

Since we now use addOrUpdateIntegration in two SDKs, I opted to move it to the utils package.

ref #7413

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.53 KB (0%)
@sentry/browser - ES5 CDN Bundle (minified)	63.85 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.19 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	56.92 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.66 KB (0%)
@sentry/browser - Webpack (minified)	72.12 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.7 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	52.05 KB (+0.07% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	33.76 KB (0%)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.13 KB (0%)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.23 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	38.28 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	62.44 KB (0%)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	55.99 KB (0%)