Allow readOnly attribute in TypedProperty OpenAPI spec (#134) (#144)

Fixes: rdar://91505904

Author: mportiz08

Sources/SwiftDocC/Model/Rendering/Symbol/PropertiesRenderSection.swift

@@ -69,6 +69,8 @@ public struct RenderProperty: Codable, TextIndexing, Equatable {
     public var required: Bool? = false
     /// If true, the property is deprecated.
     public var deprecated: Bool? = false
+    /// If true, the property can only be accessed and not modified.
+    public var readOnly: Bool? = false
     /// A version of the platform that first introduced the property, if known.
     public var introducedVersion: String?
 }

Sources/SwiftDocC/SwiftDocC.docc/Resources/RenderNode.spec.json

@@ -2800,6 +2800,9 @@
                     "mimeType": {
                         "type": "string"
                     },
+                    "readOnly": {
+                        "type": "boolean"
+                    },
                     "required": {
                         "type": "boolean"
                     },

Tests/SwiftDocCTests/Rendering/RESTSymbolsTests.swift

@@ -244,11 +244,13 @@ class RESTSymbolsTests: XCTestCase {
         XCTAssertEqual(properties.items.count, 2)
         guard properties.items.count == 2 else { return }
 
-        // The first property is not deprecated but required
+        // The first property is not deprecated/readonly but required
         XCTAssertNil(properties.items[0].deprecated)
+        XCTAssertNil(properties.items[0].readOnly)
         XCTAssertEqual(properties.items[0].required, true)
-        // The second property is deprecated but not required
+        // The second property is deprecated/readonly but not required
         XCTAssertEqual(properties.items[1].deprecated, true)
+        XCTAssertEqual(properties.items[1].readOnly, true)
         XCTAssertNil(properties.items[1].required)
 
         guard let attributes = properties.items[0].attributes else {

Tests/SwiftDocCTests/Rendering/Rendering Fixtures/rest-object.json

@@ -136,6 +136,7 @@
         {
             "name" : "status",
             "deprecated" : true,
+            "readOnly" : true,
             "type" : [
                 {
                     "kind" : "identifier",