fix(logs): remove Dispose from the public API surface area

[Flash0ver]

Summary

Remove Dispose() from SentryStructuredLogger public API surface area.

Remarks

In #4310, we added SentryStructuredLogger.Dispose(),
where only one out of three derived types actually has IDisposable fields.
This was necessary to enable cascading disposal (when Hub.IsEnabled and SentryOptions.(Experimental).EnableLogs) out of Hub.Dispose(), whose compile-time type is only the abstract SentryStructuredLogger, but not the concrete DefaultSentryStructuredLogger (because through the DisabledHub, or when EnableLogs is not true, a DisabledSentryStructuredLogger is created).

However, this allows user code to call Dispose() on the abstract SentryStructuredLogger, and therefore Dispose the concrete DefaultSentryStructuredLogger (when enabled) and its IDisposable members, without disposing any of the other Sentry instances, leaving the SDK in an inconsistent half-disposed and no longer fully usable state.

Use code can invoke:

SentrySdk.Experimental.Logger.Dispose();

The only path, where the concrete DefaultSentryStructuredLogger should be disposed, is when the CurrentHub, which creates and owns the instance of SentryStructuredLogger, is disposed.

Therefore, I'd like to remove Dispose() from the public API surface area of SentryStructuredLogger.
In order to still Dispose the DefaultSentryStructuredLogger (when enabled) when the owning Hub instance is disposed, the concrete DefaultSentryStructuredLogger still implements IDisposable and the owning Hub does a type-check on the Logger instance.

No (breaking) major release required, because SentryStructuredLogger is still [Experimental].

Changes

• Remove IDisposable from abstract SentryStructuredLogger
• Add IDisposable explicitly to DefaultSentryStructuredLogger, which owns disposable members
• Hub performs a type-check before calling Dispose() on the Logger instance that it owns

[Flash0ver]

@sentry review

[jamescrosswell]

LGTM