Rollup merge of #27699 - nathankleyn:diagnostics-383, r=Manishearth
Rollup merge of #27699 - nathankleyn:diagnostics-383, r=Manishearth

This adds detailed diagnostics for `E0383`, 'partial reinitialization of
uninitialized structure'.

This is part of rust-lang/rust#24407.

r? @Manishearth

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