fix(unity): update SentryEvent to have IsCaptured to allow dropping screenshots of filtered events

[JoshuaMoelans]

As suggested in getsentry/sentry-unity#2642 , we add a flag so we can read from it during the CaptureScreenshotCoroutine. We gate it behind #if SENTRY_UNITY to not expose it for the other .NET SDK consumers.

---

As described in the 'Future Ideas' section of the unity PR, at some point we might want to provide sentry-unity with a wrapper ISentryClient which can overwrite methods, to avoid needing changes in .NET for unity specific stuff like we need to do in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.06%. Comparing base (cd3f966) to head (75f83b8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5162   +/-   ##
=======================================
  Coverage   74.05%   74.06%           
=======================================
  Files         501      501           
  Lines       18111    18113    +2     
  Branches     3521     3521           
=======================================
+ Hits        13413    13415    +2     
  Misses       3838     3838           
  Partials      860      860           

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[Flash0ver]

thought: alternative

As an alternative, we could use our "Fused-Data" infrastructure, based on ConditionalWeakTable<,>.

e.g.

/* here */
@event.SetFused(new EnvelopeCaptureStatus(true));

/* in sentry-dotnet's ScreenshotEventProcessor */
if (a.GetFused<EnvelopeCaptureStatus>() is { IsCaptured: true })
{
    // Data found in CWT ... process and capture screenshot
}
else
{
    // no Data found in CWT ... stop processing the screenshot
}

/* new file in src/Sentry/Platforms/Unity/ */
#if SENTRY_UNITY

namespace Sentry.Internal;

internal sealed class EnvelopeCaptureStatus
{
    public EnvelopeCaptureStatus(bool isCaptured)
    {
        IsCaptured = isCaptured;
    }

    public bool IsCaptured { get; }
}

#endif

But to be fair ... now after manifesting this thought,
the "physical" property is just as good,
since it's internal and Unity-only anyway,
and also more navigable within an IDE.

I'd still like to hear feedback, though 😉

[JoshuaMoelans]

Hmm yeah that is an option, but I'm a bit more drawn towards the (maybe less elegant-) simpler "physical" property solution for now. Since it doesn't introduce any potential future breakage of a public API, it'll be easy to replace it with something better at relatively low maintenance cost in the meantime.