Restore details for Impls on Foreign Types
Restore details for Impls on Foreign Types

These were previously removed along with the details in the
"Implementors" section of trait pages. But for "Implementations on
Foreign Types," we need to include the details because they will not be
documented anywhere else.

graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust