Use pattern matching (#56532)

Use pattern matching to avoid casts.

src/Http/Http.Abstractions/src/FragmentString.cs

@@ -128,7 +128,7 @@ public override bool Equals(object? obj)
         {
             return !HasValue;
         }
-        return obj is FragmentString && Equals((FragmentString)obj);
+        return obj is FragmentString value && Equals(value);
     }
 
     /// <summary>

src/Http/Http.Abstractions/src/HostString.cs

@@ -298,7 +298,7 @@ public override bool Equals(object? obj)
         {
             return !HasValue;
         }
-        return obj is HostString && Equals((HostString)obj);
+        return obj is HostString value && Equals(value);
     }
 
     /// <summary>

src/Http/Http.Abstractions/src/Internal/HeaderSegment.cs

@@ -41,7 +41,7 @@ public override bool Equals(object? obj)
             return false;
         }
 
-        return obj is HeaderSegment && Equals((HeaderSegment)obj);
+        return obj is HeaderSegment value && Equals(value);
     }
 
     public override int GetHashCode()

src/Http/Http.Abstractions/src/Internal/HeaderSegmentCollection.cs

@@ -27,7 +27,7 @@ public override bool Equals(object? obj)
             return false;
         }
 
-        return obj is HeaderSegmentCollection && Equals((HeaderSegmentCollection)obj);
+        return obj is HeaderSegmentCollection collection && Equals(collection);
     }
 
     public override int GetHashCode()

src/Http/Http.Abstractions/src/QueryString.cs

@@ -231,7 +231,7 @@ public override bool Equals(object? obj)
         {
             return !HasValue;
         }
-        return obj is QueryString && Equals((QueryString)obj);
+        return obj is QueryString query && Equals(query);
     }
 
     /// <summary>

src/Shared/RazorViews/BaseView.cs

@@ -193,9 +193,9 @@ protected void WriteAttribute(
             // instead of the string 'true'. If the value is the bool 'false' we don't want to write anything.
             // Otherwise the value is another object (perhaps an HtmlString) and we'll ask it to format itself.
             string? stringValue;
-            if (value.Value is bool)
+            if (value.Value is bool flag)
             {
-                if ((bool)value.Value)
+                if (flag)
                 {
                     stringValue = name;
                 }