Fix struct unpacking in libraries

[palinatolmach]

Solidity unpacks struct elements in function signatures only as long as the function is not defined as part of the library, otherwise the struct is referenced by libName.structName. This PR adds an additional check on whether the contract is a library when generating a method signature to look up its selector in methodIdentifiers.

E.g., Solidity generates

_calc(DLib.InitialParams)

and not

_calc((uint256,uint256,uint256,uint256,uint256,(uint256,uint256,uint256,uint256,uint256)))

as we expected.

This PR also adds a struct and a function taking it as a parameter to an existing library in a test suite.

Note: storage is being added to the struct name if the location of the input parameter is storage; that is not implemented in this PR, I'll open a separate issue.