Replace RSAEncrypt with SSHKeyPair supporting Ed25519/ECDSA/RSA; (#1414)

- Replace RSAEncrypt with SSHKeyPair, which uses java.security.Signature
   (sign/verify) instead of Cipher (encrypt/decrypt), enabling support
   for Ed25519 and ECDSA in addition to RSA
 - Update DebugAuthenticator to use SSHKeyPair.verify()
 - Update key-gen tool with -t flag for key type selection (default: Ed25519),
   dynamically listing supported types from the KeyType enum
 - Replace RSAEncryptTest with parameterized SSHKeyPairTest covering all
   three key types
 - Only advertise declaration, definition, and hover LSP capabilities
   when StaticAnalysis is globally enabled, fixing spurious "error
   analyzing included file" diagnostics for users with SA off
 - Remove setLocalEnable(true) calls from LangServModel that were
   forcing SA on regardless of user config

Author: LadyCailin