fixes and features

[SimonCropp]

Fixes

• Fix quadratic handling of duplicate property names in JTokenWriter. A duplicate now replaces the existing property in its original position instead of moving to the end
• Throw JsonSerializationException for a non-string $type
• Detect negative zero by comparing bits rather than dividing by zero
• Fix default value population for renamed constructor parameters
• Fix "Duplicate attribute" when converting nested single item arrays to an XDocument
• Keep the json:Array marker on single item arrays whose names need XML encoding
• Support Index and list patterns on JArray
• Write comments containing "*/" as line comments
• Fix InvalidCastException comparing a BigInteger JValue with a short, ushort, byte, sbyte or enum JValue
• Set a value type member to its default when given null, instead of throwing
• Read TimeOnly with TimeOnly.Parse so "13:45" is accepted
• Drop "Required" from the DisallowNull error message
• Reduce allocations in ToMultidimensionalArray
• Throw from the serializer's dynamic paths when DynamicIsSupported is off, and honour the switch in JObject and JValue

Features

• Serialize Int128, UInt128 and Half as JSON numbers. They were previously written as strings, which are still read
• Serialize Memory and ReadOnlyMemory as arrays, or base64 when T is byte

Unions

• Ignore $id, $type, $ref and $values when matching object cases by property name
• Use $type to select a case when TypeNameHandling is enabled. TypeNameHandling.Auto now writes the type of the case
• Select the case for a $ref from the referenced object
• Treat an object holding $values as an array
• Match cases read by a converter, and object and JToken cases, against any JSON shape. An enum read by StringEnumConverter matches strings and numbers
• Read "NaN", "Infinity" and "-Infinity" into float and double cases