Revert "Make function builders internal"

This reverts commit fe3a245.

Author: akkyie

Sources/SwiftSyntaxBuilder/DeclBuildables.swift

@@ -35,8 +35,8 @@ extension DeclBuildable {
 // MARK: - Function Builder
 
 @_functionBuilder
-struct DeclListBuilder {
-  static func buildBlock(_ builders: DeclListBuildable...) -> DeclListBuildable {
+public struct DeclListBuilder {
+  public static func buildBlock(_ builders: DeclListBuildable...) -> DeclListBuildable {
     DeclList(builders: builders)
   }
 }

Sources/SwiftSyntaxBuilder/SyntaxBuildables.swift

@@ -31,8 +31,8 @@ extension SyntaxBuildable {
 // MARK: - Function Builder
 
 @_functionBuilder
-struct SyntaxListBuilder {
-  static func buildBlock(_ builders: SyntaxListBuildable...) -> SyntaxListBuildable {
+public struct SyntaxListBuilder {
+  public static func buildBlock(_ builders: SyntaxListBuildable...) -> SyntaxListBuildable {
     SyntaxList(builders: builders)
   }
 }