5e6e1e33a1
Replace simple `if let` constructs with Option::map
Replaces a few constructs of the form
```
if let Some(x) = var {
Some(...)
} else {
None
}
```
with calls to `Option::map`.
`@rustbot` modify labels +C-cleanup +T-compiler
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.