`given` does not work with literal types

`given` does not work with literal types

## Minimized code

```Scala
given s: "literal" = "literal" // compile error
```

## Output

```
an identifier expected, but string literal found
  given s: "literal" = "literal"
```

## Expectation
Should compiles.
```Scala
implicit val s: "literal" = "literal" // compiles
```
works fine.
