Refresh protocol-20-era XDR on the Stellar Transaction page (create-contract V2, smart-account credentials)

[ElliotFriend]

The XDR quoted on Stellar Transaction is protocol-20-era in several places. Surfaced while reviewing #2655, where the SorobanTransactionData reference link was pinned to a commit predating diskReadBytes. That one link is fixed; the rest of the page still needs a pass.

Comparing against v27.0/Stellar-transaction.x:

HostFunction (#invokehostfunctionop)

• Missing case HOST_FUNCTION_TYPE_CREATE_CONTRACT_V2: CreateContractArgsV2 createContractV2;
• CreateContractArgsV2 (adds SCVal constructorArgs<>) isn't documented at all, so contract constructors — protocol 22 — have no coverage here.

SorobanCredentials (#authorization-data)

• Missing SOROBAN_CREDENTIALS_ADDRESS_V2 and SOROBAN_CREDENTIALS_ADDRESS_WITH_DELEGATES / SorobanAddressCredentialsWithDelegates. Relevant to smart accounts and delegated signers.

SorobanAuthorizedFunction

• Missing SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_V2_HOST_FN.
• Shows SorobanAuthorizedContractFunction contractFn; and then defines that struct. It no longer exists in the protocol — the variant is InvokeContractArgs contractFn;.
• The prose says "SorobanAuthorizedFunction has two variants"; there are three.

HashIDPreimage

• Missing ENVELOPE_TYPE_SOROBAN_AUTHORIZATION_WITH_ADDRESS / sorobanAuthorizationWithAddress. The signature field description points readers at the plain ENVELOPE_TYPE_SOROBAN_AUTHORIZATION preimage only.

Stale reference pin

• The [xdr] link for the HostFunction / InvokeHostFunctionOp block is still pinned to e372df9, a commit old enough that it names the op BumpFootprintExpirationOp. Deliberately left alone in Correct Soroban transaction resource, TTL, and SAC XDR references #2655: repointing it at v27.0 would only expose the CREATE_CONTRACT_V2 gap above. Bump it as part of this refresh.

Each struct edit needs matching prose, so this wants a protocol-accuracy review rather than a mechanical copy-paste from the .x file.