feat: Add Proximity sample

Uno.Gallery/Uno.Gallery.Shared/Views/SamplePages/ProximitySamplePage.xaml

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+<?xml version="1.0" encoding="utf-8" ?>
+<Page x:Class="Uno.Gallery.Views.Samples.ProximitySamplePage"
+      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+      xmlns:smtx="using:ShowMeTheXAML"
+      xmlns:local="using:Uno.Gallery"
+      mc:Ignorable="d">
+	<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+		<local:SamplePageLayout IsDesignAgnostic="True">
+			<local:SamplePageLayout.DesignAgnosticTemplate>
+				<DataTemplate>
+					<StackPanel>
+						<smtx:XamlDisplay UniqueKey="ProximitySamplePage_Sample"
+						                  smtx:XamlDisplayExtensions.IgnorePath="XX"
+						                  smtx:XamlDisplayExtensions.Header="Proximity">
+<!-- C# code
+var selector = ProximitySensor.GetDeviceSelector();
+var devices = await DeviceInformation.FindAllAsync(selector);
+var device = devices.FirstOrDefault();
+if (device is not null)
+{
+
+#if __ANDROID__
+	_proximity = ProximitySensor.FromId(device.Id);
+#endif
+}
+private async void Proximity_ReadingChanged(ProximitySensor sender, ProximitySensorReadingChangedEventArgs args)
+{
+	await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
+	{
+		Distance = args.Reading.DistanceInMillimeters;
+		IsDetected = args.Reading.IsDetected;
+	});
+}
+-->
+							<StackPanel Spacing="20">
+
+								<TextBlock>
+									<LineBreak />
+									<Span FontWeight="Bold">Distance: </Span>
+									<Run Text="{Binding Data.Distance}" />
+									<Span>mm</Span>
+									<LineBreak />
+								</TextBlock>
+
+								<Button IsEnabled="{Binding Data.IsProximityAvailable}" Click="ObserveReadingChangeButton_Click">
+									<TextBlock Text="{Binding Data.ButtonContent}" VerticalAlignment="Stretch" TextAlignment="Center" />
+								</Button>
+							</StackPanel>
+						</smtx:XamlDisplay>
+					</StackPanel>
+				</DataTemplate>
+			</local:SamplePageLayout.DesignAgnosticTemplate>
+		</local:SamplePageLayout>
+	</Grid>
+
+</Page>

Uno.Gallery/Uno.Gallery.Shared/Views/SamplePages/ProximitySamplePage.xaml.cs

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+using System;
+using System.Linq;
+using Uno.Gallery.ViewModels;
+using Windows.ApplicationModel.Core;
+using Windows.Devices.Enumeration;
+using Windows.Devices.Sensors;
+using Windows.UI.Core;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using System.Threading.Tasks;
+
+namespace Uno.Gallery.Views.Samples
+{
+	[SamplePage(SampleCategory.NonUIFeatures, "Proximity",
+		Description = "Represents a Proximit sensor. This sensor returns distance.",
+		DocumentationLink = "https://platform.uno/docs/articles/features/proximity-sensor.html",
+		DataType = typeof(ProximitySamplePageViewModel))]
+	public sealed partial class ProximitySamplePage : Page
+	{
+		public ProximitySamplePage ()
+		{
+			this.InitializeComponent();
+			Loaded += ProximitySamplePage_Loaded;
+		}
+
+		private async void ProximitySamplePage_Loaded(object sender, RoutedEventArgs e)
+		{
+			if (!(((Sample)DataContext).Data is ProximitySamplePageViewModel viewModel))
+				return;
+			await viewModel.OnLoaded();
+		}
+
+		private void ObserveReadingChangeButton_Click(object sender, RoutedEventArgs e)
+		{
+			if (!(((Sample)DataContext).Data is ProximitySamplePageViewModel viewModel))
+				return;
+
+			if (!viewModel.ObservingReadingChange)
+			{
+				viewModel.StartObserveReadingChange();
+			}
+			else
+			{
+				viewModel.StopObservingReadingChange();
+			}
+		}
+	}
+
+	public class ProximitySamplePageViewModel : ViewModelBase
+	{
+		private const string _startObservingContent = "Start observing proximity reading changes";
+		private const string _stopObservingContent = "Stop observing proximity reading changes";
+		private string _notAvailable = "Proximity is not available on this device/platform";
+
+		private ProximitySensor _proximity = null;
+
+		public string ButtonContent
+		{
+			get => GetProperty<string>();
+			set => SetProperty<string>(value);
+		}
+
+		public bool IsProximityAvailable
+		{
+			get => GetProperty<bool>();
+			set => SetProperty<bool>(value);
+		}
+
+		public bool ObservingReadingChange
+		{
+			get => GetProperty<bool>();
+			set => SetProperty<bool>(value);
+		}
+
+		public uint? Distance
+		{
+			get => GetProperty<uint?>();
+			set => SetProperty<uint?>(value);
+		}
+
+		public bool IsDetected
+		{
+			get => GetProperty<bool>();
+			set => SetProperty<bool>(value);
+		}
+
+		public bool ProximityAvailable => _proximity != null;
+
+
+
+		public ProximitySamplePageViewModel()
+		{
+			IsProximityAvailable = false;
+			ButtonContent = _notAvailable;
+		}
+
+		public void StartObserveReadingChange()
+		{
+			_proximity.ReadingChanged += Proximity_ReadingChanged;
+			ButtonContent = _stopObservingContent;
+			ObservingReadingChange = true;
+		}
+
+		public void StopObservingReadingChange()
+		{
+			_proximity.ReadingChanged -= Proximity_ReadingChanged;
+			ButtonContent = _startObservingContent;
+			ObservingReadingChange = false;
+		}
+
+		private async void Proximity_ReadingChanged(ProximitySensor sender, ProximitySensorReadingChangedEventArgs args)
+		{
+			await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
+			{
+				Distance = args.Reading.DistanceInMillimeters;
+				IsDetected = args.Reading.IsDetected;
+			});
+		}
+
+		internal async Task OnLoaded()
+		{
+			var selector = ProximitySensor.GetDeviceSelector();
+			var devices = await DeviceInformation.FindAllAsync(selector);
+			var device = devices.FirstOrDefault();
+			if (device is not null)
+			{
+
+#if __ANDROID__ || !HAS_UNO
+				_proximity = ProximitySensor.FromId(device.Id);
+#endif
+			}
+
+			if (_proximity is not null)
+			{
+				await CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
+				{
+					IsProximityAvailable = true;
+					ButtonContent = _startObservingContent;
+				});
+				return;
+			}
+		}
+
+	}
+}