Auto merge of #149917 - GuillaumeGomez:malformed-attribute-suggestions, r=JonathanBrouwer

If there are too many suggestions for malformed attribute, do not suggest them

Part of rust-lang/rust#149865.

This not only covers for doc attributes but for all attributes, so don't hesitate to tell me if you want it to be limited to only doc attributes (although I think it's actually a nice improvement overall).

Also, I picked 3 as the maximum number of suggestions before it becomes noise, but it's very much open to debate.

r? `@JonathanBrouwer`

Author: bors