Added IWebHostEnvironment polyfill

Minimal implementation for `MapPathWebRoot` method.

src/Core/Hosting/AspNetFxWebHostEnvironment.cs

@@ -0,0 +1,15 @@
+#if NET472
+using Microsoft.AspNetCore.Hosting;
+using Umbraco.Core.IO;
+
+namespace Umbraco.Core.Hosting
+{
+    internal sealed class AspNetFxWebHostEnvironment : IWebHostEnvironment
+    {
+        public string MapPathWebRoot(string path)
+        {
+            return IOHelper.MapPath(path);
+        }
+    }
+}
+#endif

src/Core/Hosting/IWebHostEnvironment.cs

@@ -0,0 +1,10 @@
+#if NET472
+namespace Microsoft.AspNetCore.Hosting
+{
+    // https://github.com/dotnet/aspnetcore/blob/v6.0.0/src/Hosting/Abstractions/src/IWebHostEnvironment.cs
+    public interface IWebHostEnvironment
+    {
+        string MapPathWebRoot(string path);
+    }
+}
+#endif

src/Core/Hosting/WebHostEnvironmentExtensions.cs

@@ -0,0 +1,19 @@
+#if NET5_0
+using Microsoft.Extensions.DependencyInjection;
+using Umbraco.Cms.Web.Common.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Hosting
+{
+    // https://github.com/umbraco/Umbraco-CMS/blob/v10/contrib/src/Umbraco.Web.Common/Extensions/WebHostEnvironmentExtensions.cs
+    internal static class WebHostEnvironmentExtensions
+    {
+        public static string MapPathWebRoot(this IWebHostEnvironment webHostEnvironment, string path)
+        {
+            var hostingEnvironment = StaticServiceProvider.Instance
+                .GetRequiredService<Umbraco.Cms.Core.Hosting.IHostingEnvironment>();
+
+            return hostingEnvironment.MapPathWebRoot(path);
+        }
+    }
+}
+#endif

src/Core/Runtime/UmbracoPolyfillComposer.cs

@@ -1,4 +1,5 @@
 #if NET472
+using Microsoft.AspNetCore.Hosting;
 using Umbraco.Core.Composing;
 using Umbraco.Core.Hosting;
 using Umbraco.Core.IO;
@@ -17,6 +18,8 @@ public void Compose(Composition composition)
 
             composition.RegisterUnique<IHostingEnvironment, AspNetFxHostingEnvironment>();
 
+            composition.RegisterUnique<IWebHostEnvironment, AspNetFxWebHostEnvironment>();
+
             composition.RegisterUnique<IIOHelper, IOHelperPolyfill>();
 
             composition.RegisterUnique<IJsonSerializer, UmbracoPolyfillJsonSerializer>();