Set default fingerprint for ANR v2 events to correctly group background and foreground ANRs

[romtsn]

📜 Description

Ideally we would do this server-side, but built-in server-side fingerprint rules are still WIP, so I think we can get away with doing it on the SDK side for now. We only set the fingerprint if user hasn't defined their custom rules to not override them.

💡 Motivation and Context

Multiple internal reports from customers

💚 How did you test it?

Manually + automated

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	392.92 ms	458.69 ms	65.77 ms
Size	1.70 MiB	2.27 MiB	583.71 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
8ff8fd0	432.77 ms	495.18 ms	62.41 ms
86f0096	368.63 ms	446.92 ms	78.29 ms
c7e2fbc	377.85 ms	426.35 ms	48.50 ms
2a3dd50	363.61 ms	440.18 ms	76.57 ms
0bd723b	375.20 ms	452.41 ms	77.20 ms
2465853	400.64 ms	465.47 ms	64.83 ms
4e29063	364.08 ms	445.51 ms	81.43 ms
4e260b3	388.40 ms	468.98 ms	80.58 ms
e6ffd7b	379.52 ms	449.30 ms	69.78 ms
c7e2fbc	393.98 ms	478.24 ms	84.27 ms

App size

Revision	Plain	With Sentry	Diff
8ff8fd0	1.72 MiB	2.27 MiB	558.15 KiB
86f0096	1.72 MiB	2.29 MiB	576.50 KiB
c7e2fbc	1.72 MiB	2.29 MiB	576.40 KiB
2a3dd50	1.72 MiB	2.27 MiB	555.05 KiB
0bd723b	1.72 MiB	2.29 MiB	578.09 KiB
2465853	1.70 MiB	2.27 MiB	583.82 KiB
4e29063	1.72 MiB	2.29 MiB	578.38 KiB
4e260b3	1.72 MiB	2.27 MiB	554.95 KiB
e6ffd7b	1.72 MiB	2.29 MiB	579.13 KiB
c7e2fbc	1.72 MiB	2.29 MiB	576.40 KiB