Remove duplication of parsing helper

Author: JunTaoLuo

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

@@ -6,13 +6,13 @@
 
 namespace Microsoft.AspNetCore.Http.Internal
 {
-    internal struct HeaderSegment : IEquatable<HeaderSegment>
+    public struct HeaderSegment : IEquatable<HeaderSegment>
     {
         private readonly StringSegment _formatting;
         private readonly StringSegment _data;
 
         // <summary>
-        // Initializes a new instance of the <see cref="HeaderSegment/> structure.
+        // Initializes a new instance of the <see cref="HeaderSegment"/> structure.
         // </summary>
         public HeaderSegment(StringSegment formatting, StringSegment data)
         {

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

@@ -8,7 +8,7 @@
 
 namespace Microsoft.AspNetCore.Http.Internal
 {
-    internal struct HeaderSegmentCollection : IEnumerable<HeaderSegment>, IEquatable<HeaderSegmentCollection>
+    public struct HeaderSegmentCollection : IEnumerable<HeaderSegment>, IEquatable<HeaderSegmentCollection>
     {
         private readonly StringValues _headers;
 
@@ -62,7 +62,7 @@ IEnumerator IEnumerable.GetEnumerator()
             return GetEnumerator();
         }
 
-        internal struct Enumerator : IEnumerator<HeaderSegment>
+        public struct Enumerator : IEnumerator<HeaderSegment>
         {
             private readonly StringValues _headers;
             private int _index;

src/Microsoft.AspNetCore.Http.Abstractions/Internal/ParsingHelpers.cs

@@ -8,7 +8,7 @@
 
 namespace Microsoft.AspNetCore.Http.Internal
 {
-    internal static class ParsingHelpers
+    public static class ParsingHelpers
     {
         public static StringValues GetHeader(IHeaderDictionary headers, string key)
         {