Fix transactions with an app start time

[krystofwoldrich]

Description

Do not add app starts that began a long time before a transaction

I could not reproduce the behavior but I've seen it happening in customers apps. Sometimes app start from 30 minutes/an hour ago would be added to a transaction. We should not add the app start time if it's not close to the start of the transaction and remove it from memory.

Do not add app start times spans longer than a threshold

We drop measurements longer than 60s but not spans, we should drop the spans too.
Current limit:

sentry-react-native/src/js/tracing/reactnativetracing.ts

Line 121 in 1887b19

private static _maxAppStart: number = 60000;