Assertion message when Sentry is loaded twice in app

[philipphofmann]

Description

We fixed loading Sentry integration from the same binary with #4541, but when Sentry is loaded twice it still could happen that Sentry isn't working correctly. It would be great to detect this in the SDK, and consider logging an error or doing an assert to crash the app in debug. We had a customer who didn't realize they loaded Sentry twice, and it they didn't receive any crash reports cause the client was nil in the SentryCrashReportSink

sentry-cocoa/Sources/Sentry/SentryCrashReportSink.m

Lines 78 to 82 in 166d67a

	SENTRY_LOG_ERROR(
	@"Crash reports were found but no [SentrySDK.currentHub getClient] is set. "
	@"Cannot send crash reports to Sentry. This is probably a misconfiguration, "
	@"make sure you set the client with [SentrySDK.currentHub bindClient] before "
	@"calling startCrashHandlerWithError:.");

[kahest]

Escalating critical issues such as this is captured in #4467

[kahest]

We should log an error when we detect that the SDK has been loaded twice (doesn't need to be an assert)