Support possible values inside property enums. (#1041)

With this change enum values that appear in the Properties section will render the allowed values they support under the enum type.

This was being rendered before and was removed in [a08f470](a08f470)

rdar://136542713

Author: sofiaromorales

Sources/SwiftDocC/Model/Rendering/RenderNodeTranslator.swift

@@ -1928,6 +1928,9 @@ public struct RenderNodeTranslator: SemanticVisitor {
             if let constraint = symbol.maximumLength {
                 attributes.append(RenderAttribute.maximumLength(String(constraint)))
             }
+            if let constraint = symbol.allowedValues {
+                attributes.append(RenderAttribute.allowedValues(constraint.map { String($0) } ))
+            }
             if let constraint = symbol.typeDetails, constraint.count > 0 {
                 // Pull out the base-type details.
                 typeDetails = constraint.filter { $0.baseType != nil }

Tests/SwiftDocCTests/Model/SemaToRenderNodeDictionaryDataTests.swift

@@ -203,8 +203,16 @@ class SemaToRenderNodeDictionaryDataTests: XCTestCase {
         XCTAssertEqual(genreProperty.name, "genre")
         XCTAssertTrue(genreProperty.readOnly ?? false)
         attributeTitles = genreProperty.attributes?.map{$0.title.lowercased()}.sorted() ?? []
-        XCTAssertEqual(attributeTitles, ["default value"])
-        genreProperty.attributes?.forEach { attribute in
+        XCTAssertEqual(attributeTitles, ["default value", "possible values"])
+        let genrePropertyAttributes = try XCTUnwrap(genreProperty.attributes)
+        let genrePropertyAllowedValues = genrePropertyAttributes.filter {
+            switch $0 {
+            case .allowedValues(_): return true
+            default: return false
+            }
+        }
+        XCTAssertEqual(genrePropertyAllowedValues.count, 1)
+        genrePropertyAllowedValues.forEach { attribute in
             if case let .allowedValues(values) = attribute {
                 XCTAssertEqual(values.count, 3)
                 XCTAssertEqual(values[0], "Classic Rock")