AbstractGenericSignatureRequest tries to minimize the number of GSBs that we
spin up by only creating a GSB if the generic parameter and requirement types
are canonical. If they're not canonical, it first canonicalizes them, then
kicks off a request to compute the canonical signature, and finally, re-applies
type sugar.
We would do this by building a mapping for re-sugaring generic parameters,
however this mapping was only populated for the newly-added generic parameters.
If some of the newly-added generic requirements mention the base signature's
generic parameters, they would remain canonicalized.
Fixes <rdar://problem/67579220>.