Codeblock tag helper improvements

[vedxyz]

Tested with this sample

                <codeblock>heyo</codeblock>
                <codeblock class="mt-2" language="csharp">
                    using System;
                    using System.Linq;
                    using System.Text.RegularExpressions;
                    using System.Threading.Tasks;
                    using Microsoft.AspNetCore.Html;
                    using Microsoft.AspNetCore.Mvc.Rendering;
                    using Microsoft.AspNetCore.Razor.TagHelpers;
                            
                    namespace OpenTabletDriver.Web.TagHelpers
                    {
                        [HtmlTargetElement("codeblock")]
                        public class CodeBlockTagHelper : TagHelper
                        {
                            public string Language { set; get; } = "plaintext";

                            public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
                            {
                                output.TagName = "pre";

                                var rawContent = (await output.GetChildContentAsync()).GetContent();
                                var body = TrimBaseIndentation(rawContent);

                                var code = new TagBuilder("code");
                                code.AddCssClass("hljs");
                                code.AddCssClass($"language-{Language}");
                                code.InnerHtml.SetHtmlContent($"{body}\n");

                                output.Content.SetHtmlContent(code);
                            }

                            private string TrimBaseIndentation(string content)
                            {
                                var endsTrimmedContent = TrimStartRegex.Replace(content.TrimEnd(), "$1", 1);
                                var lines = endsTrimmedContent.Split(Environment.NewLine);
                                var baseIndentationLength = CountIndentation(lines[0]);

                                for (int i = 0; i != lines.Length; i++)
                                {
                                    var line = lines[i];

                                    var indentationLength = CountIndentation(line);
                                    if (indentationLength < baseIndentationLength)
                                    {
                                        if (indentationLength == line.Length)
                                        {
                                            lines[i] = "";
                                            continue;
                                        }

                                        return endsTrimmedContent;
                                    }

                                    lines[i] = line.Substring(Math.Min(baseIndentationLength, line.Length));
                                }

                                return String.Join(Environment.NewLine, lines).Trim();
                            }
                            
                            static private Regex TrimStartRegex = new("^\\s*\n(\\s*)(?=\\S*)", RegexOptions.Compiled);

                            private int CountIndentation(string line) => line.TakeWhile(Char.IsWhiteSpace).Count();
                        }
                    }

                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    
                    if (true) {
                        Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                        Console.WriteLine("Hey!");
                    }
                    
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    
                    if (true) {
                        Console.WriteLine("Hey!");
                    }
                    
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    
                    
                    if (true) {
                        Console.WriteLine("Hey!");
                    }
                    
                    
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {

                        Console.WriteLine("Hey!");

                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    
                    if (true) {

                        Console.WriteLine("Hey!");

                    }
                    
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                        Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">if (true) {
                        Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                        Console.WriteLine("Hey!");
                    }</codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                    Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
if (true) {
    Console.WriteLine("Hey!");
}
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                    if (true) {
                        Console.WriteLine("Hey!");
                }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
                if (true) {
                        Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">
        if (true) {
                        Console.WriteLine("Hey!");
                    }
                </codeblock>
                <codeblock class="mt-2" language="csharp">if (true) { Console.WriteLine("Hey!"); }
                </codeblock>
                <codeblock class="mt-2" language="csharp">if (true) { Console.WriteLine("Hey!"); }</codeblock>

Also tested with existing codeblocks.
Appears to be working smoothly on all instances.

Changes

• Add default language plaintext to the tag helper
• Remove redundant addition of hljs class
• Replace indentation trimming implementation

[vedxyz]

Rebased to resolve conflicts and optimize CountIndentation