Auto merge of #121657 - estebank:issue-119665, r=davidtwco

Detect more cases of `=` to `:` typo

When a `Local` is fully parsed, but not followed by a `;`, keep the `:` span arround and mention it. If the type could continue being parsed as an expression, suggest replacing the `:` with a `=`.

```
error: expected one of `!`, `+`, `->`, `::`, `;`, or `=`, found `.`
 --> file.rs:2:32
  |
2 |     let _: std::env::temp_dir().join("foo");
  |          -                     ^ expected one of `!`, `+`, `->`, `::`, `;`, or `=`
  |          |
  |          while parsing the type for `_`
  |          help: use `=` if you meant to assign
```

Fix #119665.

Author: bors