Rollup merge of #53777 - ivanbakel:result_map_or_else, r=alexcrichton
Rollup merge of #53777 - ivanbakel:result_map_or_else, r=alexcrichton

Implemented map_or_else for Result<T, E>

Fulfills #53268
The example is ripped from `Option::map_or_else`, with the types corrected.

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