[Java.Interop] Map nullable byte jagged arrays to java.lang.Byte

[simonrozsival]

Summary

• treat byte? as a managed-to-JNI signature alias of sbyte? for java/lang/Byte in the reflection type manager built-ins
• preserve Java-to-managed canonicalization of java/lang/Byte as sbyte?
• cover rank-2 and rank-3 nullable byte jagged arrays in legacy and trimmable type-manager/device tests

Experiment evidence

Before this change, legacy reverse signature lookup had no built-in entry for System.Byte?. Looking up byte?[][] or byte?[][][] therefore failed, and JNIEnv.NewArray() fell back to java.lang.Object[][] / java.lang.Object[][][]. The element values still round-tripped. The trimmable manager already returned the intended [[Ljava/lang/Byte; and [[[Ljava/lang/Byte; signatures.

Behavior change

Legacy byte? reverse lookup now shares the existing nullable signed-byte JNI signature, producing exact java.lang.Byte array classes at ranks 2 and 3. Primitive byte/sbyte behavior, Java-to-managed sbyte? canonicalization, and collection roots are unchanged.

Tests

• dotnet test tests/Java.Interop-Tests/Java.Interop-Tests.csproj --filter FullyQualifiedName~JniTypeManagerTests (6 passed; supplied installed JDK paths)
• added device coverage for exact rank-2/rank-3 JNI class names and managed value round-trips; device tests were not run locally