Use special strings for methodSig to handle contract call by pre-compiled ABI data

[songge-cb]

Motivation

This PR is to add some logic to the preprocess API to handle fallback pattern contract call. This type of contract call does not have a method signature.

Solution

We will use either empty string or a unique string "NO-METHOD-SIG" to indicate it. The pre-compiled ABI data will be passed in as methodArgs, either in the string format or the first element of an array.

Testing

• Tested Preprocess API locally by passing empty string and "NO-METHOD-SIG" as methodSig.

Open questions

[cb-heimdall]

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