Use Trivia(joining:) in SyntaxCollections

We've introduced `Trivia(joining: [Trivia], separator: [Trivia])` to
generate doc comments from multiple pieces, and already use this
approach in `SyntaxNodesFile` for nodes themselves, and for node
children documentation.

This commit switches from joining pieces manually to using
`Trivia(joining:)` in `SyntaxCollectionsFile` so that we use the same
approach everywhere.

Author: natikgadzhi

CodeGeneration/Sources/SyntaxSupport/GrammarGenerator.swift

@@ -70,7 +70,7 @@ struct GrammarGenerator {
   /// token.
   static func childTokenChoices(for choices: [TokenChoice]) -> String {
     let grammar = GrammarGenerator()
-    
+
     if choices.count == 1 {
       return """
         ### Tokens

CodeGeneration/Sources/SyntaxSupport/Utils.swift

@@ -58,15 +58,16 @@ extension SwiftSyntax.Trivia {
     return SwiftSyntax.Trivia(pieces: pieces)
   }
 
-
   /// Make a new trivia by joining together ``SwiftSyntax/TriviaPiece``s from `joining`,
   /// and gluing them together with pieces from `separator`.
   public init(
     joining items: [SwiftSyntax.Trivia],
-    separator: SwiftSyntax.Trivia = SwiftSyntax.Trivia(pieces: [TriviaPiece.newlines(1), TriviaPiece.docLineComment("///"), TriviaPiece.newlines(1)])) {
+    separator: SwiftSyntax.Trivia = SwiftSyntax.Trivia(pieces: [TriviaPiece.newlines(1), TriviaPiece.docLineComment("///"), TriviaPiece.newlines(1)])
+  ) {
 
     self.init(
-      pieces: items
+      pieces:
+        items
         .filter { !$0.isEmpty }
         .joined(separator: separator)
     )

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/SyntaxCollectionsFile.swift

@@ -17,18 +17,11 @@ import Utils
 
 let syntaxCollectionsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
   for node in SYNTAX_NODES.compactMap(\.collectionNode) {
-    let documentationSections = [
+    let documentation = SwiftSyntax.Trivia(joining: [
       node.documentation,
       node.grammar,
       node.containedIn,
-    ]
-
-    let documentation =
-      documentationSections
-      .filter { !$0.isEmpty }
-      .map { [$0] }
-      .joined(separator: [Trivia.newline, Trivia.docLineComment("///"), Trivia.newline])
-      .reduce(Trivia(), +)
+    ])
 
     try! StructDeclSyntax(
       """