Soroban counter.sol example

[salaheldinsoliman]

This PR aims to make Solang support a simple counter.sol example on Soroban, where a storage variable is instatiated, modified and retrieved. The counter contract is only limited to uint64 data types, and only supports instance soroban storage.

This can be considered a "skeleton" for supporting more data and storage types, as well as more host function invokations.

• Support Soroban storage function calls put_contract_data, get_contract_data and has_contract_data
• Implement a wrapper init for storage_initializer
• Implement wrappers for public functions
• Insert decoding/encoding instructions into the wrapper functions
• Soroban doesn't have function return codes. This needs to be handled all over emit
• Add integration tests and MockVm tests