Create system for registering custom LiteralConverters (#269)

Motivation
----------
Extensions may need to control serialization and deserialization of literals beyond the types including in-box.

Modifications
-------------
- Define `LiteralConverter` and `LiteralConverter<T>` abstract base types for converters
- Create `LiteralConverterRegistry` for registering converters
- Create converters for all currently supported types and register them automatically
- Rewrite `LiteralSerializer` to use the singleton from `LiteralConverterRegistry.Instance`
- Add `System.Collections.Immutable` as a dependency on generated SDKs when targeting downlevel frameworks to get access to `FrozenDictionary`

Breaking Changes
----------------
The namespace of `LiteralSerializer` is changed to `XXX.Serialization.Literals` in generated SDKs.

Results
-------
A more extensible framework for extensions that want to support additional types in headers, path parameters, and query strings. A potential future use is an extension for NodaTime type support.

SDK consumers that need to customize serialization may also do so by mutating the public `LiteralConverterRegistry.Instance`.

Also fixes a bug deserializing nullable enums from literals.

Resolves #268
Fixes #267

src/main/Directory.Packages.props

@@ -16,6 +16,7 @@
     <PackageVersion Include="NuGet.Commands" Version="6.11.1" />
     <PackageVersion Include="Serilog.Extensions.Logging" Version="8.0.0" />
     <PackageVersion Include="Serilog.Sinks.Console" Version="6.0.0" />
+    <PackageVersion Include="System.Collections.Immutable" Version="8.0.0" />
     <PackageVersion Include="System.Linq.Async" Version="6.0.1" />
     <PackageVersion Include="System.Net.Http.Json" Version="8.0.1" />
     <PackageVersion Include="System.Net.Primitives" Version="4.3.1" />

src/main/Yardarm.Client.UnitTests/Serialization/LiteralSerializerTests.cs

@@ -1,6 +1,6 @@
 using System;
 using FluentAssertions;
-using RootNamespace.Serialization;
+using RootNamespace.Serialization.Literals;
 using Xunit;
 
 namespace Yardarm.Client.UnitTests.Serialization
@@ -888,6 +888,18 @@ public void Deserialize_Enum_ReturnsValue()
             result.Should().Be(StringComparison.Ordinal);
         }
 
+        [Fact]
+        public void Deserialize_NullableEnum_ReturnsValue()
+        {
+            // Act
+
+            StringComparison? result = LiteralSerializer.Deserialize<StringComparison?>("Ordinal");
+
+            // Assert
+
+            result.Should().Be(StringComparison.Ordinal);
+        }
+
         #endregion
 
         #region JoinListT

src/main/Yardarm.Client/Serialization/HeaderSerializer.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using RootNamespace.Serialization.Literals;
 using Yardarm.Client.Internal;
 
 // ReSharper disable once CheckNamespace

src/main/Yardarm.Client/Serialization/Literals/Converters/BooleanLiteralConverter.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace RootNamespace.Serialization.Literals.Converters;
+
+internal sealed class BooleanLiteralConverter : ValueTypeLiteralConverter<bool>
+{
+    protected override bool ReadCore(string value, string? format) =>
+        bool.Parse(value);
+
+    public override string Write(bool value, string? format) => value ? "true" : "false";
+
+#if NET6_0_OR_GREATER
+
+    public override bool TryWrite(bool value, ReadOnlySpan<char> format, Span<char> destination, out int charsWritten)
+    {
+        var boolString = value ? "true" : "false";
+        if (boolString.TryCopyTo(destination))
+        {
+            charsWritten = boolString.Length;
+            return true;
+        }
+
+        charsWritten = 0;
+        return false;
+    }
+
+#endif
+}

src/main/Yardarm.Client/Serialization/Literals/Converters/ByteLiteralConverter.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace RootNamespace.Serialization.Literals.Converters;
+
+internal sealed class ByteLiteralConverter : ValueTypeLiteralConverter<byte>
+{
+    // CultureInfo.InvariantCulture is not needed for unsigned integers
+
+    protected override byte ReadCore(string value, string? format) =>
+        byte.Parse(value);
+
+    public override string Write(byte value, string? format) =>
+        value.ToString();
+
+#if NET6_0_OR_GREATER
+
+    public override bool TryWrite(byte value, ReadOnlySpan<char> format, Span<char> destination, out int charsWritten) =>
+        value.TryFormat(destination, out charsWritten);
+
+#endif
+}

src/main/Yardarm.Client/Serialization/Literals/Converters/DateTimeLiteralConverter.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Globalization;
+
+namespace RootNamespace.Serialization.Literals.Converters;
+
+internal sealed class DateTimeLiteralConverter : ValueTypeLiteralConverter<DateTime>
+{
+    protected override DateTime ReadCore(string value, string? format) =>
+        format switch
+        {
+            "date" or "full-date" => DateTime.ParseExact(value, "yyyy-MM-dd", CultureInfo.InvariantCulture),
+            _ => DateTime.Parse(value, CultureInfo.InvariantCulture)
+        };
+
+    public override string Write(DateTime value, string? format) =>
+        format switch
+        {
+            "date" or "full-date" => value.ToString("yyyy-MM-dd"),
+            _ => value.ToString("O")
+        };
+
+#if NET6_0_OR_GREATER
+
+    public override bool TryWrite(DateTime value, ReadOnlySpan<char> format, Span<char> destination, out int charsWritten) =>
+        format switch
+        {
+            "date" or "full-date" => value.TryFormat(destination, out charsWritten, format: "yyyy-MM-dd"),
+            _ => value.TryFormat(destination, out charsWritten, format: "O")
+        };
+
+#endif
+}