test(replay): Streamline replay test imports

[mydea]

This PR does some further streamlining of replay test code.
Specifically, it tries to avoid mocking of code with jest as much as possible, only doing so when necessary.

Also, it introduces an autoStart argument to mockSdk, which can be used to make the SDK not start automatically. As this can make some tests weird/brittle. (Currently, only one test, but maybe more tests could use this).

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.68 KB (-0.02% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.96 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.47 KB (0%)
@sentry/browser - ES6 CDN Bundle (minified)	54.51 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	20.27 KB (0%)
@sentry/browser - Webpack (minified)	66.25 KB (0%)
@sentry/react - Webpack (gzipped + minified)	20.29 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	47.29 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	26.67 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.12 KB (+0.01% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	41.83 KB (+0.1% 🔺)
@sentry/replay - Webpack (gzipped + minified)	37.89 KB (+0.03% 🔺)