Add multiselect with search and better display

[Masterjun3]

This adds a TagHelper that can be used with the <select> element. For non-javascript people, the old way still works.

2023-08-26.18-00-05.mp4

Usage is like this:

<select asp-for="Search.GameGroups" size="@(Math.Min(Model.AvailableGameGroups.Count(), 7).ToString())" asp-items="Model.AvailableGameGroups" class="form-control"></select>
<select-improver select-id="@Html.IdFor(m => m.Search.GameGroups)"></select-improver>