docs: Update the typing RFC with info about wildcards
docs: Update the typing RFC with info about wildcards

Resolves #10726.

This change details the specification levels of desired types in the
Summer RFC. Specifically, it discusses unspecified and partially-specified
desired types. This does not actually affect the typing algorithm at
all, as wildcard type preferences simply replace the option to pass no
type preference as a desired type. However, by unifying the notions of
"AnyType" in function signatures and unspecified type preferences during
type checking, our existing typing algorithm can support a broader set of
builtin functions without ambiguity.

glycerine/cockroach,maxlang/cockroach,vaibhavarora/cockroach,petermattis/cockroach,maxlang/cockroach,veteranlu/cockroach,paperstreet/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,glycerine/cockroach,petermattis/cockroach,maxlang/cockroach,paperstreet/cockroach,veteranlu/cockroach,glycerine/cockroach,glycerine/cockroach,veteranlu/cockroach,veteranlu/cockroach,maxlang/cockroach,petermattis/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,maxlang/cockroach,petermattis/cockroach,glycerine/cockroach,glycerine/cockroach,glycerine/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,petermattis/cockroach,petermattis/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,petermattis/cockroach,veteranlu/cockroach,glycerine/cockroach,vaibhavarora/cockroach,petermattis/cockroach,veteranlu/cockroach,maxlang/cockroach,vaibhavarora/cockroach,paperstreet/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach