Create BaseGalleryPage

[TheCodeTraveler]

Description

This PR creates BaseGalleryPage.cs that can be used for each Gallery Page.

This removes the duplicate code that currently exists in BehaviorGalleryPage and ConvertersGalleryPage, allowing us to easily implement Gallery pages:

public class ConvertersGalleryPage : BaseGalleryPage<ConvertersGalleryViewModel>
{
  public ConvertersGalleryPage() : base("Converters")
  {
  }
}

BaseGalleryPage.cs will make it super easy to add new Gallery pages in the future, like ViewsGalleryPage, ExtensionsGalleryPage, etc.

BaseGalleryPage.cs uses the same style found in the existing gallery pages:

Detailed Solution

• Add CommunityToolkit.Maui.Markup NuGet Package
• Create BehaviorsGalleryPage.cs
  • A CollectionView to display BaseGalleryViewModel.Items
  • BehaviorsGalleryPage.cs is implemented using C# Markup Extensions because XAML ContentPages cannot be inherited
• Remove bottom Padding in MainPage.xaml.cs
  • MainPage uses a ScrollView which needs to extend to the bottom of the page
• Simplify BehaviorsGalleryPage
  • Inherit from BaseGalleryPage
• Simplify ConvertersGalleryPage
  • Inherit from BaseGalleryPage