Add [GeneratedCode] and [ExcludeFromCodeCoverage] to Name Generator output members

[stevemonaco]

What does the pull request do?

Adds attributes to output of both Name Generators (InitializeComponentCodeGenerator and OnlyPropertiesCodeGenerator).

• Generated fields now have the [GeneratedCode] attribute.
• Generated InitializeComponent method now has [GeneratedCode] and [ExcludeFromCodeCoverage]

What is the updated/expected behavior with this PR?

Code generated by InitializeComponentCodeGenerator now looks like:

namespace Sandbox
{
    partial class MainWindow
    {
        [global::System.CodeDom.Compiler.GeneratedCode("Avalonia.Generators.NameGenerator.InitializeComponentCodeGenerator", "11.2.999.0")]
        internal global::Avalonia.Controls.Grid grid;
        [global::System.CodeDom.Compiler.GeneratedCode("Avalonia.Generators.NameGenerator.InitializeComponentCodeGenerator", "11.2.999.0")]
        internal global::Avalonia.Controls.TextBlock text;

        /// <summary>
        /// Wires up the controls and optionally loads XAML markup and attaches dev tools (if Avalonia.Diagnostics package is referenced).
        /// </summary>
        /// <param name="loadXaml">Should the XAML be loaded into the component.</param>
        /// <param name="attachDevTools">Should the dev tools be attached.</param>

        [global::System.CodeDom.Compiler.GeneratedCode("Avalonia.Generators.NameGenerator.InitializeComponentCodeGenerator", "11.2.999.0")]
        [global::System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
        public void InitializeComponent(bool loadXaml = true, bool attachDevTools = true)
        {
            if (loadXaml)
            {
                AvaloniaXamlLoader.Load(this);
            }

#if DEBUG
            if (attachDevTools)
            {
                this.AttachDevTools();
            }
#endif

            var __thisNameScope__ = this.FindNameScope();
            grid = __thisNameScope__?.Find<global::Avalonia.Controls.Grid>("grid");
            text = __thisNameScope__?.Find<global::Avalonia.Controls.TextBlock>("text");
        }
    }
}

How was the solution implemented (if it's not obvious)?

I mostly tried to match what Mvvm Toolkit is doing for its output, though this generator is still on ISourceGenerator instead of incremental. Code strings were built similar to the existing parts of the generators instead of Roslyn AST.

The unit tests and unit test data required updating. The version parameter of [GeneratedCode] will be ever-changing, so a $GeneratorVersion tag was used in test code files. Mvvm Toolkit uses <ASSEMBLY_VERSION> with a similar replacement strategy at test-time.

Checklist

• Updated unit tests

Breaking changes

None

Fixed issues

Fixes #15611

[cla-avalonia]

• All contributors have signed the CLA.

[stevemonaco]

@cla-avalonia agree

[avaloniaui-bot]

You can test this PR using the following package version. 11.2.999-cibuild0048102-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]