feat(core): Allow to pass mechanism as event hint

[mydea]

This allows to pass mechanism as an event hint. Also, we now allow to pass hint as an alternative to CaptureContext to captureException as second argument.

We have quite a lot of code where we fork a scope and add an event processor, only to add a mechanism to the event.
Since this is a quite common pattern, I figured it makes more sense to allow to pass a mechanism as an EventHint.

In addition, I noticed that while hub.captureException() takes an event hint as second argument, in the core exported captureException() we take a CaptureContext as second argument instead (for legacy reasons).

In order to be able to pass a mechanism there as well, I updated the method signature to allow either a CaptureContext or an EventHint. I wrote some tests covering this to make sure that works - it's a bit tricky since both can be POJOs, but no fields overlap so we are able to parse this together.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	66.02 KB (+0.12% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	56.1 KB (+0.14% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.1 KB (+0.27% 🔺)
@sentry/browser - Webpack (gzipped)	21.41 KB (+0.39% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	62.42 KB (+0.1% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	29.23 KB (+0.29% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	21.35 KB (+0.35% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	196.93 KB (+0.16% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	88.74 KB (+0.35% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	63.71 KB (+0.49% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	31.96 KB (+0.3% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	66.31 KB (+0.12% 🔺)
@sentry/react - Webpack (gzipped)	21.45 KB (+0.39% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	83.08 KB (+0.11% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	48.25 KB (+0.18% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	16.19 KB (+0.55% 🔺)