perf(core): Use build-time class availability

[romtsn]

📜 Description

Allow LoadClass.isClassAvailable to use class-availability results supplied by build tooling before falling back to Class.forName. The lookup map is nullable and private, so applications without compatible tooling keep the existing reflection behavior.

💡 Motivation and Context

Android SDK initialization probes optional integrations reflectively. Build tooling already knows whether their owning modules are present, so it can avoid those runtime checks.

Refs JAVA-654

💚 How did you test it?

• ./gradlew spotlessApply apiDump
• ./gradlew :sentry:test --tests '*LoadClassTest*'
• Pixel 2 XL microbenchmark: map construction and lookups were about 160× faster than the equivalent absent-heavy 11-class reflection batch.
• In the absent-heavy startup macrobenchmark, SDK initialization was 1.08% faster and full startup was 0.88% faster, though variance exceeded the measured delta. The representative 10-present/1-absent case showed no measurable improvement.

📝 Checklist

• I added GH Issue ID & Linear ID
• 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.
• I updated the wizard 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.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.

🔮 Next steps

getsentry/sentry-android-gradle-plugin#1375 injects the build-time results.

#skip-changelog

[linear-code]

JAVA-654

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.51.0 (1)	release

⚙️ sentry-android Build Distribution Settings

[runningcode]

Seems simple enough!