feat: add source generator with basic attribute generation

[erictuvesson]

Input:

namespace Mallos.Searchable.Test
{
    using Mallos.Searchable.Attributes;
    using System;

    [FilterGenerator("MyGeneratedSearchable")]
    public class TestObject
    {
        [FilterKey("v"), FilterStringMatch(FilterMatchType.Match)]
        [FilterKey("value"), FilterStringMatch(FilterMatchType.Contains, StringComparison.OrdinalIgnoreCase)]
        public string Value { get; set; }

        [FilterKey("key"), FilterStringMatch()]
        public string Key { get; set; }

        public TestObject(string value)
        {
            this.Value = value;
        }
    }
}

Generated Output:

using Mallos.Searchable;
using Mallos.Searchable.Attributes;
using System;
using System.Collections.Generic;
using Mallos.Searchable.Test;

public class MyGeneratedSearchableFilter_FilterStringMatch_v : SimpleFilter<TestObject> 
{
    public override string Key => "v";

    protected override bool Check(TestObject item, string value)
    {
        return Mallos.Searchable.Attributes.FilterStringMatchAttribute.Execute(
            item.Value,
            value,
            FilterMatchType.Match
        );
    }
}

public class MyGeneratedSearchableFilter_FilterStringMatch_value : SimpleFilter<TestObject> 
{
    public override string Key => "value";

    protected override bool Check(TestObject item, string value)
    {
        return Mallos.Searchable.Attributes.FilterStringMatchAttribute.Execute(
            item.Value,
            value,
            FilterMatchType.Contains,
            StringComparison.OrdinalIgnoreCase
        );
    }
}

public class MyGeneratedSearchableFilter_FilterStringMatch_key : SimpleFilter<TestObject> 
{
    public override string Key => "key";

    protected override bool Check(TestObject item, string value)
    {
        return Mallos.Searchable.Attributes.FilterStringMatchAttribute.Execute(
            item.Key,
            value
        );
    }
}

public class MyGeneratedSearchable : Searchable<TestObject> 
{
    public MyGeneratedSearchable()
    {
        Filters.Add(new MyGeneratedSearchableFilter_FilterStringMatch_v());
        Filters.Add(new MyGeneratedSearchableFilter_FilterStringMatch_value());
        Filters.Add(new MyGeneratedSearchableFilter_FilterStringMatch_key());
    }

    protected override IEnumerable<TestObject> FreeTextFilter(
        IEnumerable<TestObject> values, bool negative, string text)
    {
        return base.FreeTextFilter(values, negative, text);
    }
}

[erictuvesson]

Have to solve the issue where the Mallos.Searchable.CodeAnalyzer project can reference this by only netstandard2.0.

I would like to add .NET 5 support here too, to be able to work with records.

[erictuvesson]

It would be nice to be able to remove this, then we don't have to depend on Mallos.Searchable project.

But how can it work without using Reflection if we don't know more about the syntax?