Make comparison faster between `SyntaxToken.type` and `SyntaxKind.rawValue`
Make comparison faster between `SyntaxToken.type` and `SyntaxKind.rawValue`

Contain `SyntaxKind.rawValue` instance instead of `type: String` parameter instance into `SyntaxToken.type`.
This makes comparison faster in some functions. e.g. `commentRangeBeforeOffset(_:)`

Duration of linting KeychainAccess by SwiftLint 0.5.2
before:
```
time swiftlint
…
swiftlint  7.96s user 0.14s system 95% cpu 8.481 total
```

after:
```
swiftlint  5.25s user 0.09s system 93% cpu 5.683 total
```

jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten,jpsim/SourceKitten