Fix Struct and Interface Syntax Issues

- Multiline comma not highlighted in structs e.g. the `,` isn't highlighted:
```go
type Foo struct {
    A,
    B string
}
```
- Semicolons not highlighted in interfaces
- Embedded type with tag not highlighted as type, e.g. `Bar` isn't highlighted as a type:
```go
type Foo struct {
    Bar `json:"bar"`
}
```