What?

browserTracingIntegration no longer captures performance.mark() / performance.measure() spans by default. This behavior moves into a new opt-in userTimingSpansIntegration, and the ignorePerformanceApiSpans option is replaced by the integration's ignore option.

// before
Sentry.init({
  integrations: [
    Sentry.browserTracingIntegration({ ignorePerformanceApiSpans: ['third-party-mark'] }),
  ],
});

// after
Sentry.init({
  integrations: [
    Sentry.browserTracingIntegration(),
    Sentry.userTimingSpansIntegration({ ignore: ['third-party-mark'] }),
  ],
});

Why?

User Timing spans are useful for some apps and pure noise for others (browser extensions and third-party libraries emit their own mark/measure entries). Bundling them into browserTracingIntegration meant everyone paid the bundle-size and span-volume cost whether they wanted the data or not, and the only escape hatch was an ignore-list. Making it a separate, explicitly-added integration means you opt in when you want it, and it drops out of the tree-shaken bundle when you don't.

Closes #22352