[github actions] Add custom source validator

.github/workflows/source_validator.yml

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+name: Source Validator
+
+on:
+  push:
+    branches:
+      - master
+      - develop
+
+jobs:
+  source_validator:
+    runs-on: ubuntu-latest
+    if: "!contains(format('{0} {1}', github.event.head_commit.message, github.event.pull_request.title), '[ci-skip]')"
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v3
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v2
+      with:
+        dotnet-version: 6.0.x
+
+    - name: Add GitHub NuGet source
+      run: dotnet nuget add source --username oliverbooth --password ${{ secrets.GITHUB_TOKEN }} --store-password-in-clear-text --name github "https://nuget.pkg.github.com/oliverbooth/index.json"
+
+    - name: Restore dependencies
+      run: dotnet restore
+
+    - name: Build
+      run: dotnet build -c Debug
+
+    - name: Run Source Validation
+      run: dotnet run --project X10D.SourceValidator ./X10D/src
+

X10D.SourceValidator/Program.cs

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+using System.Text;
+
+var directories = new Stack<string>(Directory.GetDirectories(args[0]));
+var problems = 0;
+var files = 0;
+
+while (directories.Count > 0)
+{
+    string path = Path.GetFullPath(directories.Pop());
+
+    foreach (string directory in Directory.EnumerateDirectories(path))
+    {
+        directories.Push(directory);
+    }
+
+    foreach (string file in Directory.EnumerateFiles(path, "*.cs"))
+    {
+        files++;
+        await using var stream = File.OpenRead(file);
+        using var reader = new StreamReader(stream, Encoding.UTF8);
+
+        var lineNumber = 1;
+        while (await reader.ReadLineAsync() is { } line)
+        {
+            if (line.Length > 130)
+            {
+                Console.ForegroundColor = ConsoleColor.Red;
+                Console.Out.WriteLine($"{file}({lineNumber}): Line is too long ({line.Length})");
+                Console.ResetColor();
+                problems++;
+            }
+            else if (line.Length > 0 && char.IsWhiteSpace(line[^1]))
+            {
+                Console.ForegroundColor = ConsoleColor.Red;
+                Console.Out.WriteLine($"{file}({lineNumber}): Line contains trailing whitespace");
+                Console.ResetColor();
+                problems++;
+            }
+
+            lineNumber++;
+        }
+    }
+}
+
+Console.Out.WriteLine($"Finished scanning {files} files, {problems} problems encountered.");
+return problems;

X10D.SourceValidator/X10D.SourceValidator.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net6.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\X10D\X10D.csproj"/>
+    </ItemGroup>
+
+</Project>