Use errorCode/SQLState from Java exceptions in stack signatures (case-insensitive @ext lookup) #2680

Problem

ErrorSignature.AddSpecialCaseDetails adds Number and ErrorCode from an error's extended data (@ext) to the signature, so database errors with different codes get different stacks: ErrorSignature.cs#L202-L213.

The lookup is case-sensitive and only knows the .NET property names. The Java client sends exception properties under their Java bean names. So for java.sql.SQLException, @ext contains errorCode and sqlState, neither of which matches. For example, a MySQL duplicate-key error (errorCode 1062) and a deadlock (errorCode 1213) thrown from the same repository method end up in the same stack.

Proposal

• Look up @ext keys case-insensitively (StringComparer.OrdinalIgnoreCase), so errorCode matches ErrorCode.
• Also use SQLState when present (sqlState from JDBC; SqlState from Npgsql.PostgresException and MySqlException on .NET). It's the portable error class across JDBC drivers and makes useful signatures for Postgres errors.

Notes

• This changes the signature hash for errors that carry these properties, so existing stacks for them will split once.
• The client could rename the keys instead, but a case-insensitive server lookup covers every client (Java, Kotlin, and anything else that sends camelCase) without special cases.

Context: exceptionless/Exceptionless.Java#91