Adjust the RPC service for the WASM-browser use case (#3013)

* Use SpawnTaskHandle to pass to the RPC

* Create the RPC server in lib.rs

* Create the RPC servers in a separate function

* Keep a local version of the RPC handlers

* Make rpc-servers compile for WASM

* Add RpcSesssion

* Clean up

* Address review

* Address pull request review