use Locale.ENGLISH for address folding in SignedMailValidator

[rootvector2]

SignedMailValidator folds both sides of the comparison that ties a signature to the sender the message claims, the certificate's email addresses in getEmailAddresses and the From addresses in hasAnyFromAddress, with Locale.getDefault() captured in a static field at class load, so on a Turkish or Azerbaijani JVM I lower cases to the dotless ı and a legitimately signed message is reported as emailFromCertMismatch while a certificate whose emailAddress attribute carries U+0130 (the attribute is read through ASN1String, not restricted to IA5String) folds onto a different mailbox and satisfies the check for it; found sweeping every module's src/main for case conversion used in a security comparison, which turned up this as the only default-locale one, the JSSE HostnameUtil, BCSNIHostName and DisabledAlgorithmConstraints all fixing Locale.ENGLISH and the EST hostname authorizer using the locale-independent Strings.toLowerCase.

AI tooling was used to help prepare this change.