* accounts/abi: prevent recalculation of ID, Sig and String

* accounts/abi: fixed unpacking of no values

* accounts/abi: multiple fixes to arguments

* accounts/abi: refactored methodName and eventName

This commit moves the complicated logic of how we assign method names
and event names if they already exist into their own functions for
better readability.

* accounts/abi: prevent recalculation of internal

In this commit, I changed the way we calculate the string
representations, sig representations and the id's of methods. Before
that these fields would be recalculated everytime someone called .Sig()
.String() or .ID() on a method or an event.

Additionally this commit fixes issue #20856 as we assign names to inputs
with no name (input with name "" becomes "arg0")

* accounts/abi: added unnamed event params test

* accounts/abi: fixed rebasing errors in method sig

* accounts/abi: fixed rebasing errors in method sig

* accounts/abi: addressed comments

* accounts/abi: added FunctionType enumeration

* accounts/abi/bind: added test for unnamed arguments

* accounts/abi: improved readability in NewMethod, nitpicks

* accounts/abi: method/eventName -> overloadedMethodName