Make CodeGeneration a lot less string-based

Because of its Python legacy the CodeGeneration tool has been heavily string-based. This PR fixes that at least to some degree.

The main motivating factors here were:
- Instead of using strings to specify the node type of a child node, define a `SyntaxNodeKind` enum that contains a case for each syntax node. This way you can be sure that you’re not referring to a non-existent syntax node (like we did for e.g. `InOutToken`, which we forgot to change to `.token("inout")`)
- Refactor `Node` so that it contains two initializers: One for collections and one for layout nodes instead of having one initializer that has a bunch of optional and defaulted arguments.
- Change a bunch of properties from returning a `String` to returning a `TypeSyntax` or `TokenSyntax` so we don‘t need to use the `raw:` interpolation style for them.

In general, the API of `Node` and `SyntaxNodeKind` is what I’m happy with now. The other files can still do with some cleanup.

All the changes resulted in nearly no functionaly changes of the generated code.

Author: ahoppen

CodeGeneration/Package.swift

@@ -20,6 +20,7 @@ let package = Package(
       dependencies: [
         .product(name: "SwiftSyntax", package: "swift-syntax"),
         .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
+        .product(name: "SwiftBasicFormat", package: "swift-syntax"),
         .product(name: "ArgumentParser", package: "swift-argument-parser"),
         "SyntaxSupport",
         "Utils",
@@ -29,11 +30,16 @@ let package = Package(
       ]
     ),
     .target(
-      name: "SyntaxSupport"
+      name: "SyntaxSupport",
+      dependencies: [
+        .product(name: "SwiftSyntax", package: "swift-syntax"),
+        .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
+      ]
     ),
     .target(
       name: "Utils",
       dependencies: [
+        .product(name: "SwiftBasicFormat", package: "swift-syntax"),
         .product(name: "SwiftSyntax", package: "swift-syntax"),
         .product(name: "SwiftSyntaxBuilder", package: "swift-syntax"),
         "SyntaxSupport",