Rollup merge of #39960 - lukaramu:issue-39925, r=alexcrichton
Rollup merge of #39960 - lukaramu:issue-39925, r=alexcrichton

added Error and Display impl for std::ffi::FromBytesWithNulError

Fixes #39925.

This is my first PR, so I wasn't quite sure about the stability annotation.

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