Soroban improvements

1. Soroban Server improvements:

• add getAccountand getContractData methods
• add missing fields oldestLedger and latestLedger to the get health response
• add useful xdr conversions: ledgerEntryData and keyVal for LedgerEntry
• add useful xdr conversions: xdrTransactionEnvelope, xdrTransactionResult, xdrTransactionMeta for GetTransactionResponse
• add missing field txHash to EventInfo
• add useful xdr conversion: valueXdr to EventInfo
• improve simulate transaction result: xdr and auth are not nullable any more

2. SEP-11 (TxRep):

• add soroban support

3. XDR helper methods

• multiple useful additional helper methods in the soroban and classic XDR classes.

4. Breaking changes:

• renamed Row to OrderBookRow for the order book response
• typo: renamed statusChangesto stateChanges for the soroban simulate transaction response