Make ~/ resolution show up at design time.

- This change results in proper errors for tags that utilize `~/`inside of local functions at design time.
- Updated TagHelper in code blocks analyzer error to mention `~/` since it will typically be a cause of confusion.

#10734

src/Mvc/Mvc.Analyzers/src/DiagnosticDescriptors.cs

@@ -59,7 +59,7 @@ namespace Microsoft.AspNetCore.Mvc.Analyzers
             new DiagnosticDescriptor(
                 "MVC1006",
                 "Methods containing TagHelpers must be async and return Task.",
-                "The method contains a TagHelper and therefore must be async and return a Task.",
+                "The method contains a TagHelper and therefore must be async and return a Task. For instance, usage of ~/ typically results in a TagHelper and requires an async Task returning parent method.",
                 "Usage",
                 DiagnosticSeverity.Error,
                 isEnabledByDefault: true);

src/Mvc/Mvc.Razor/ref/Microsoft.AspNetCore.Mvc.Razor.netcoreapp3.0.cs

@@ -356,7 +356,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
     [Microsoft.AspNetCore.Razor.TagHelpers.HtmlTargetElementAttribute("track", Attributes="[src^='~/']", TagStructure=Microsoft.AspNetCore.Razor.TagHelpers.TagStructure.WithoutEndTag)]
     [Microsoft.AspNetCore.Razor.TagHelpers.HtmlTargetElementAttribute("video", Attributes="[poster^='~/']")]
     [Microsoft.AspNetCore.Razor.TagHelpers.HtmlTargetElementAttribute("video", Attributes="[src^='~/']")]
-    [System.ComponentModel.EditorBrowsableAttribute(System.ComponentModel.EditorBrowsableState.Never)]
     public partial class UrlResolutionTagHelper : Microsoft.AspNetCore.Razor.TagHelpers.TagHelper
     {
         public UrlResolutionTagHelper(Microsoft.AspNetCore.Mvc.Routing.IUrlHelperFactory urlHelperFactory, System.Text.Encodings.Web.HtmlEncoder htmlEncoder) { }

src/Mvc/Mvc.Razor/src/TagHelpers/UrlResolutionTagHelper.cs

@@ -50,7 +50,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
     [HtmlTargetElement("track", Attributes = "[src^='~/']", TagStructure = TagStructure.WithoutEndTag)]
     [HtmlTargetElement("video", Attributes = "[src^='~/']")]
     [HtmlTargetElement("video", Attributes = "[poster^='~/']")]
-    [EditorBrowsable(EditorBrowsableState.Never)]
     public class UrlResolutionTagHelper : TagHelper
     {
         // Valid whitespace characters defined by the HTML5 spec.