gh-114258: Refactor Argument Clinic function name parser (#114930)

gh-114258: Refactor Argument Clinic function name parser (#114930)

Refactor state_modulename_name() of the parsing state machine, by
adding helpers for the sections that deal with ...:

1. parsing the function name
2. normalizing "function kind"
3. dealing with cloned functions
4. resolving return converters
5. adding the function to the DSL parser