Make CodableContentSection.section property public (#1344)

* Make CodableContentSection.section public

This allows other applications linking to Swift DocC to access this property.

* Modernize how section property initializes its stored property using an init accessor

Author: mayaepps

Sources/SwiftDocC/Model/Rendering/RenderNode/CodableContentSection.swift

@@ -15,7 +15,11 @@ import Foundation
 /// This allows decoding a ``RenderSection`` into its appropriate concrete type, based on the section's
 /// ``RenderSection/kind``.
 public struct CodableContentSection: Codable, Equatable {
-    var section: any RenderSection {
+    public var section: any RenderSection {
+        @storageRestrictions(initializes: typeErasedSection)
+        init(initialValue)  {
+            typeErasedSection = AnyRenderSection(initialValue)
+        }
         get {
             typeErasedSection.value
         }
@@ -27,15 +31,13 @@ public struct CodableContentSection: Codable, Equatable {
 
     /// Creates a codable content section from the given section.
     public init(_ section: any RenderSection) {
-        self.typeErasedSection = AnyRenderSection(section)
         self.section = section
     }
 
     public init(from decoder: any Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)
         let kind = try container.decode(RenderSectionKind.self, forKey: .kind)
 
-        self.typeErasedSection = AnyRenderSection(ContentRenderSection(kind: .content, content: []))
         switch kind {
             case .discussion:
                 section = try ContentRenderSection(from: decoder)