Emit description for SyntaxCollections as doc comments

Author: ahoppen

Sources/SwiftSyntax/SyntaxCollections.swift.gyb

@@ -31,6 +31,11 @@ public protocol SyntaxCollection: SyntaxProtocol, Sequence {
 /// `${node.collection_element_type}` nodes. ${node.name} behaves
 /// as a regular Swift collection, and has accessors that return new
 /// versions of the collection with different children.
+% if node.description:
+%   for line in dedented_lines(node.description):
+/// ${line}
+%   end
+% end
 public struct ${node.name}: SyntaxCollection, SyntaxHashable {
   public let _syntaxNode: Syntax
 

Sources/SwiftSyntax/gyb_generated/SyntaxCollections.swift

@@ -1492,6 +1492,10 @@ extension DeclNameArgumentListSyntax: BidirectionalCollection {
 /// `ExprSyntax` nodes. ExprListSyntax behaves
 /// as a regular Swift collection, and has accessors that return new
 /// versions of the collection with different children.
+/// 
+/// A list of expressions connected by operators. This list is contained
+/// by a `SequenceExprSyntax`.
+/// 
 public struct ExprListSyntax: SyntaxCollection, SyntaxHashable {
   public let _syntaxNode: Syntax
 
@@ -4432,6 +4436,7 @@ extension PatternBindingListSyntax: BidirectionalCollection {
 /// `EnumCaseElementSyntax` nodes. EnumCaseElementListSyntax behaves
 /// as a regular Swift collection, and has accessors that return new
 /// versions of the collection with different children.
+/// A collection of 0 or more `EnumCaseElement`s.
 public struct EnumCaseElementListSyntax: SyntaxCollection, SyntaxHashable {
   public let _syntaxNode: Syntax
 
@@ -6147,6 +6152,9 @@ extension AttributeListSyntax: BidirectionalCollection {
 /// `Syntax` nodes. SpecializeAttributeSpecListSyntax behaves
 /// as a regular Swift collection, and has accessors that return new
 /// versions of the collection with different children.
+/// 
+/// A collection of arguments for the `@_specialize` attribute
+/// 
 public struct SpecializeAttributeSpecListSyntax: SyntaxCollection, SyntaxHashable {
   public let _syntaxNode: Syntax