fix(core): Avoid using Object.values()

[mydea]

This is not downcompiled for ES5 (=it is still present this way in the bundle.es5.js files - see e.g. https://browser.sentry-cdn.com/7.41.0/bundle.es5.js and search for Object.values()). So instead we use Object.keys() (which works in IE11) here.

Fixes #7354

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.12 KB (+0.01% 🔺)
@sentry/browser - ES5 CDN Bundle (minified)	62.55 KB (+0.05% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.76 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	55.53 KB (+0.02% 🔺)
@sentry/browser - Webpack (gzipped + minified)	20.5 KB (+0.03% 🔺)
@sentry/browser - Webpack (minified)	66.99 KB (+0.02% 🔺)
@sentry/react - Webpack (gzipped + minified)	20.53 KB (+0.03% 🔺)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.2 KB (+0.01% 🔺)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.2 KB (-0.02% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	25.46 KB (+0.01% 🔺)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	42.87 KB (0%)
@sentry/replay - Webpack (gzipped + minified)	36.93 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	60.62 KB (-0.01% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	54 KB (0%)