Fix type parameter default error to mention type and trait definitions
Fix type parameter default error to mention type and trait definitions

Introduced in PR #30724, needs to mention that type parameter defaults
are legal in trait and type definitions too.

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