Fix add missing thread name/id to app start spans

[markushi]

📜 Description

As these spans are synthetic, they don't get enriched with thread info. Given that all of them run on the main thread, it should be safe to directly add the main thread info to them.

💡 Motivation and Context

💚 How did you test it?

📝 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	386.04 ms	412.58 ms	26.54 ms
Size	1.70 MiB	2.28 MiB	588.11 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
0810952	364.51 ms	468.08 ms	103.57 ms
2fad834	390.07 ms	470.80 ms	80.73 ms
2465853	422.61 ms	491.20 ms	68.58 ms
8ff8fd0	432.77 ms	495.18 ms	62.41 ms
2465853	400.64 ms	465.47 ms	64.83 ms
5e04ee8	365.26 ms	448.49 ms	83.23 ms
c554ca2	368.52 ms	430.74 ms	62.22 ms
4e29063	384.14 ms	447.74 ms	63.60 ms
0404ea3	394.73 ms	461.79 ms	67.06 ms
0404ea3	332.47 ms	401.12 ms	68.66 ms

App size

Revision	Plain	With Sentry	Diff
0810952	1.72 MiB	2.27 MiB	558.21 KiB
2fad834	1.72 MiB	2.29 MiB	577.53 KiB
2465853	1.70 MiB	2.27 MiB	583.82 KiB
8ff8fd0	1.72 MiB	2.27 MiB	558.15 KiB
2465853	1.70 MiB	2.27 MiB	583.82 KiB
5e04ee8	1.70 MiB	2.27 MiB	584.64 KiB
c554ca2	1.70 MiB	2.27 MiB	582.25 KiB
4e29063	1.72 MiB	2.29 MiB	578.38 KiB
0404ea3	1.72 MiB	2.29 MiB	577.52 KiB
0404ea3	1.72 MiB	2.29 MiB	577.52 KiB