Soroban improvements

1. Soroban Server improvements:

• add getAccount and getContractData methods
• add missing fields type and txHash to EventInfo
• add useful xdr conversionvalueXdrto EventInfo
• add missing fields latestLager and oldestLedger to GetHealthResponse
• add useful xdr conversions transactionEnvelope, transactionResult and transactionMeta to GetTransactionResponse
• add useful xdr conversions keyXdrValueand valueXdr to LedgerEntry
• add missing resultErrorXdr field to SendTransactionResponse
• make costoptional in SimulateTransactionResponse as it has been marked as deprecated in the RPC API docs.
• make xdr and auth fields not nullable in SimulateTransactionResult

2. TxRep (SEP-11):

• add soroban support