Implements Default for mutable slices. Fixes: #29244
Implements Default for mutable slices. Fixes: #29244

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