Clarify Application class code and system splash screen vs. Android TTID

[sentry-junior]

The Android app-start docs (docs/platforms/android/tracing/instrumentation/automatic-instrumentation.mdx, Cold Start / Time to Initial Display sections) don't clarify two behaviors that came up in a customer question:

• Code in the Application class (e.g. onCreate, attachBaseContext) runs before TTID ends and is counted as part of cold start, not after it. This follows from SentryPerformanceProvider's ContentProvider.onCreate() starting the app-start clock, which itself runs before Application.onCreate().
• The Android system splash screen (the default SplashScreen API window on Android 12+, shown as an OS-rendered Window rather than an Activity) has no effect on TTID measurement. The SDK has no splash-screen-specific instrumentation (verified: no splash/SplashScreen references anywhere in sentry-java); TTID is purely Activity-lifecycle- and first-frame-drawn-based.

Adding a short note covering both points to the Cold Start / TTID docs would help customers reason about what does and doesn't count toward the measurement.

Requested by kpujji via Junior.

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View Junior Session in Sentry

[linear-code]

DOCS-2909