[mayuki]

This PR improves rendering of XML documentation comments in help output.

This change adds support for rendering character entity references such as > and <, as well as elements such as <a> and <br />. Constructs that are difficult to represent, such as <see cref="..."/>, are ignored.

Example source code

public class MyClass
{
    /// <summary>
    /// &lt;hello &amp; world&gt;. <see cref="System.Console.WriteLine(string)"/>
    ///      Line1
    /// Line2<br />
    /// <a href="https://cysharp.co.jp/">Cysharp</a>|<see paramref="boo"/>|<see langword="null" />|<br />
    /// <c>code</c>|<b>bold</b>|<i>italic</i>|<u>underline</u>|///
    /// <para>paragraph<br/>paragraph L2<br /><a href="https://link.example/">Example</a></para>
    /// </summary>
    /// <param name="boo">-b, my boo is not <c>boo</c>.|&lt;&amp;&gt;</param>
    /// <param name="fooBar">-f|-fb, my foo, is not <b>bar</b>.|&lt;&amp;&gt;</param>
    public async Task HelloWorld([Argument]int boo, string fooBar)
    {
        Console.Write("Hello World! " + fooBar);
    }
}

Result

Usage: hello-world [arguments...] [options...] [-h|--help] [--version]

<hello & world>. Line1 Line2
Cysharp (https://cysharp.co.jp/)|boo|null|
code|bold|italic|underline|///
paragraph
paragraph L2
Example (https://link.example/)

Arguments:
  [0] <int>    my boo is not boo.|<&>

Options:
  -f, -fb, --foo-bar <string>    my foo, is not bar.|<&> [Required]

[neuecc]

thanks, perfect!