Auto merge of #45741 - oli-obk:refactor_suggestions, r=estebank

Refactor internal suggestion API

~~The only functional change is that whitespace, which is suggested to be added, also gets `^^^^` under it. An example is shown in the tests (the only test that changed).~~

Continuation of #41876

r? @nagisa

the changes are probably best viewed [without whitespace](https://github.com/rust-lang/rust/pull/45741/files?w=1)

diff --cc src/librustc_errors/emitter.rs
Simple merge

diff --cc src/libsyntax/json.rs
Simple merge