Rollup merge of #134474 - oli-obk:push-yomnkntvzlxw, r=compiler-errors

Forbid overwriting types in typeck

While trying to figure out some type setting logic in rust-lang/rust#134248 I realized that we sometimes set a type twice. While hopefully that would have been the same type, we didn't ensure that at all and just silently accepted it. So now we reject setting it twice, unless errors are happening, then we don't care.

Best reviewed commit by commit.

No behaviour change is intended.