Add builtin to extend TTL for Soroban storage variables

[salaheldinsoliman]

Soroban has a mechanism that ensures the active ledger state doesn't grow indefinitely. Every stored contract key has a certain TTL (Time to Live) that can be extended by calling a Soroban host function.

This can be handled by adding a Solang builtin extend_ttl(var).

Relative docs: https://developers.stellar.org/docs/build/guides/storage/choosing-the-right-storage