Improve DX for Script class

[arboleya]

It should follow the same DX we have on Contract, supporting things like:

• txParams
• callParams
• getTransactionRequest
• Etc.

This increases flexibility and ease of use, giving users complete control of everything.

Related:

• Improve DX for Predicate class #1457

[danielbate]

Given we already have access to the invocation scope for a Script in the same way we'd expect to access it for a Contract (i.e. script.functions.main(argument)), we already have access to the same transaction preparation DX. However we should look to improve the documentation on this.