use ContentControl with template for TemplateColumn

[w-ahmad]

Fixes #188 and might also address #211.

This PR updates the way cell content is loaded in a template column. Previously, the content was manually set after loading the template using DataTemplate.LoadContent(), which caused issues with x:Bind and Binding.Converters. The new approach uses a ContentControl with the cell template, which is then used as the cell content.

[Copilot]

Pull Request Overview

This PR fixes issues with data binding in template columns by replacing direct template content loading with ContentControl-based rendering. The change ensures that x:Bind and Binding.Converters work correctly in template columns by leveraging the proper data binding infrastructure.

• Updated GenerateElement to use ContentControl with ContentTemplate instead of DataTemplate.LoadContent()
• Updated GenerateEditingElement to use the same ContentControl approach for editing templates
• Maintains existing fallback behavior when editing templates are not defined

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