[release/10.0] Fix Native AOT-incompatible reflection in CalendarTestBase

[Copilot]

Change #122373 broke native AOT testing because it introduced trimming incompatible code into a test.

/cc @MichalStrehovsky

Customer Impact

• Customer reported
• Found internally

Test only change. We broke release/10.0 using a release/10.0-only change.

Regression

• Yes
• No

Testing

Outerloop run.

Risk

Low. Test only.

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• For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).

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[MichalStrehovsky]

/azp run runtime-nativeaot-outerloop

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Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull request overview

This PR aims to restore NativeAOT test compatibility by adjusting reflection usage in the Japanese calendar test infrastructure (CalendarTestBase) on release/10.0, after a prior change introduced trimming/AOT-incompatible reflection patterns.

Changes:

• Reworks reflection used to compute the ICU-specific JapaneseCalendar minimum supported date (era ticks) to be more NativeAOT-friendly.

[Copilot]

Type.GetType(string) is annotated with RequiresUnreferencedCode on CoreCLR, so this line will produce trimming/AOT analyzer warnings (and likely fail NativeAOT test builds). Consider avoiding Type.GetType(...) here; you can obtain the EraInfo element type via the reflected GetEraInfo method signature (e.g., from MethodInfo.ReturnType.GetElementType()), which avoids string-based type lookup and the RUC annotation.

Suggested change

	object[] eraInfo = (object[])typeof(JapaneseCalendar).GetMethod("GetEraInfo", BindingFlags.NonPublic | BindingFlags.Static)!.Invoke(null, null)!;
	Type eraInfoType = Type.GetType("System.Globalization.EraInfo, System.Private.CoreLib")!;
	MethodInfo getEraInfoMethod = typeof(JapaneseCalendar).GetMethod("GetEraInfo", BindingFlags.NonPublic | BindingFlags.Static)!;
	object[] eraInfo = (object[])getEraInfoMethod.Invoke(null, null)!;
	Type eraInfoType = getEraInfoMethod.ReturnType.GetElementType()!;