SVM: add a sample stand-alone application based on SVM

[dmakarov]

Problem

SVM API enables development of advanced applications based on Solana execution engine. Writing such applications from scratch is a non-trivial task currently requiring knowledge of Solana run-time internals. A real-life SVM based example application is helpful for developers to jump-start working with SVM. An example presented in this PR is a client-server pair of applications that demonstrate using SVM to develop a Json-RPC server that responds to transaction simulation requests from a client program.

Summary of Changes

Add an extended example to the SVM crate

• json-rpc-server is a server application that implements several Solana Json RPC commands, in particular simulateTransaction command to run a transaction in minimal Solana run-time environment required to use SVM.
• json-rpc-client is a sample client application that submits simulateTransaction requests to json-rpc server.
• json-rpc-program is source code of an on-chain program executed in the context of the simultateTransaction command submitted by the client program.

[dmakarov]

@joncinque, @pgarg66 This is still a very early draft, as I'm working on cleaning up the code and integrating this example in CI.

[buffalojoec]

@dmakarov the refactoring is looking great! Let me know when this is ready for another look.

[dmakarov]

I'm going to merge this now with the intention to continue improving this in follow-up PRs, which seems to be more manageable.