feat: Provide the exception in the Hint passed to BeforeBreadcrumb

[jamescrosswell]

Summary

When a breadcrumb is created from an exception, the exception itself is now provided in the SentryHint passed to the SetBeforeBreadcrumb callback, under a new HintTypes.Exception key.

This mirrors the Java SDK, which puts the originating logging event into the Hint it passes to beforeBreadcrumb (see TypeCheckHint, e.g. logback:loggingEvent). Until now .NET only ever passed an empty hint for these, so a BeforeBreadcrumb callback could only filter exception breadcrumbs by string-matching the message.

options.SetBeforeBreadcrumb((breadcrumb, hint) =>
    hint.Items.TryGetValue(HintTypes.Exception, out var exception) && exception is MyException
        ? null       // drop it
        : breadcrumb);

Covered sites:

• Hub.AddBreadcrumbForException — the automatic Exception breadcrumb left on the scope for every captured exception event.
• Sentry.Extensions.Logging, Sentry.Serilog, Sentry.NLog and Sentry.Log4Net — breadcrumbs those integrations create for log entries that carry an exception (i.e. below MinimumEventLevel, where they don't defer to the Hub's breadcrumb).

Notes for review

• HubExtensions gains a hint-carrying overload of the [EditorBrowsable(Never)] AddBreadcrumb(clock, …) method that the logging integrations use. It's a new overload rather than an added optional parameter, to avoid a binary-breaking change and overload ambiguity at existing call sites.
• The Net4_8 API approval snapshot was hand-edited, since that TFM can't be built on macOS. The other three regenerated normally.

Relates to #5514. It does not close that issue: this gives users a way to filter exception breadcrumbs by type, but the SDK still leaves a breadcrumb for an exception that its own IExceptionFilter just dropped. That needs a separate change to AddBreadcrumbForException so it respects SentryOptions.ExceptionFilters.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.79%. Comparing base (fd638f0) to head (2f8d0ed).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5523      +/-   ##
==========================================
+ Coverage   74.75%   74.79%   +0.04%     
==========================================
  Files         515      515              
  Lines       18884    18903      +19     
  Branches     3688     3690       +2     
==========================================
+ Hits        14116    14139      +23     
+ Misses       3884     3883       -1     
+ Partials      884      881       -3     

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